I'm assuming a knowledge of Infinity War (because cba to explain all of that) but I'll do my best to explain all the references to previous MCU movies for those who have not seen them or cannot remember. There were a lot, which was really delightful to see- I never really realised how much lore Marvel had built up until this film. Some weren't direct references but continuations of themes or character arcs, so I have a section for that below the Easter eggs.
OBVIOUSLY SPOILER ALERT YOU HAVE BEEN WARNED
EASTER EGGS AND REFERENCES IN CHRONOLOGICAL ORDER
1. Captain Marvel shows up to rescue Tony:
So, the Avengers found the pager that Nick Fury used to summon Carol [as seen in the Infinity War post-credits scene] and she showed up in New York [as seen in the Captain Marvel post credits scene]. We can assume that the Avengers tell her to find Tony and Nebula based on Tony's messages. So we never actually see Carol meet the Avengers which is a bit of a shame.
2. Tony drifts off to sleep:
We hear elements of the score that eventually plays at his funeral. That isn't an Easter egg, it's just a cool musical motif.
3. 'To his garden':
Thanos actually did start up a farm in the Infinity Gauntlet comic, as seen in the image above. The scarecrow made out of his armour is from one of the panels, in fact. MCU Thanos has nothing on those boots.
4. The man talking about a date he went on in Captain America's support group is co-director, Joe Russo, and another member is played by Jim Starlin, writer of the original comic! Also, the fact that Steve Rogers is leading a support session may be a callback to Sam Wilson (Falcon) leading a PTSD/veteran session in Captain America: Winter Soldier.
5. Since Disney owns Pixar as well, is the rat that activates the van Remy from Ratatouille? I choose to think so...
6. Ant-Man's return:
For those that missed Ant-Man and the Wasp's post credit scene, Scott (Paul Rudd) gets stuck in the 'quantum realm' after his friends get snapped away by Thanos. In this film, we see him reunite with his daughter, Cassie, who was very young in the first two Ant-Man movies. (We also get a hint of Christophe Beck's Ant-Man theme music! I wrote about how Marvel rarely re-use their themes so I was delighted to see some continuity here.)
7. Carol Danver's new hairdo is straight from her modern run in the comics and it excited me more than I can say.
8. Scott says to Tony Stark that they won't 'bet on any sporting events' which is a reference to Back to the Future Part 2, as Tony calls out, where Biff acquires a sport magazine from the future and makes a lot of money by betting on the winning teams.
9. More of a running joke, but Ant-Man always calls Steve Rogers by the full 'Captain America', which started during their first meeting in Captain America: Civil War.
10. Rocket and Hulk travel to New Asgard:
In the events of Thor Ragnarok, we see Thor's homeworld of Asgard destroyed. So, the surviving Asgardians have set up camp on Earth, in the location that Thor's father, Odin, recommended they make their new home before his passing. During this sequence, we also see the return of fan favourite Ragnarok characters Valkyrie, Korg and Miek.
11. Hawkeye killing a bunch of people:
A pull from the 'Ultimate' line of comics (which is an alternate universe type of deal) where losing his family makes Clint Barton adopt the persona of 'Ronan', a ninja warrior.
12. Tony calls Thor 'Lebowski' which is a reference to 'The Dude' from The Big Lebowski, played by Jeff Bridges, who also played the baddie in the first Iron Man.
13. Thor drunkenly describing the reality stone:
Thor basically explains the plot of Thor: The Dark World to the rest of the team. More on this later, but the movie has Jane infected by the reality stone and Thor's mother dying. And Loki dying. But not for real. Not yet.
[Time travel starts]
14. Events of the first Avengers in 2012:
Tony, Steve, Bruce and Scott travel to 2012 to steal the Tesseract (the space stone)- which had been stolen from SHIELD by Loki- as well as Loki's sceptor which contained the mind stone. The Time Stone is also here since, as explained in the plot of Doctor Strange, it has always been guarded by the sorcerors in New York. Bruce encounters the Ancient One (Tilda Swinton), a powerful sorceror who later trains Stephen Strange (Benedict Cumberbatch).
Next, we get an insight into what happened after the events of the Avenger's battle, with a lot of cool SHIELD related cameos. The people who get out of the lift are secret Hydra agents, Rumlow and Sitwell, as revealed in Captain America: The Winter Soldier. We also see secret Hydra leader, Alexander Pierce (Robert Redford), in one of the more surprising cameos of the film.
The elevator scene:
As many will have noticed, this is a partial recreation of the brilliant Winter Soldier elevator scene, with some of the dialogue, sound effects and shots mirroring the original. Steve saying 'Hail Hydra'- apart from being freaking hilarious- is also a reference to an infamous panel of a recent comic where Captain America was revealed to be a secret Hydra agent (incidentally, that story also included a Captain America vs Captain America fight!).
Loki escaping is presumably a set up for his newly announced TV show on Disney+
'I could do this all day':
Present-Cap quickly dismisses this line with a quick 'I know' because this has been a repeated quote throughout Captain America's solo films.
15. Events of Thor: The Dark World 2013:
We see Loki in a jail cell playing catch, which is a shot taken directly from TDW. Past-Thor has brought Jane to Asgard to try and remove the reality stone liquid from her blood, which is what Rocket tries to extract. At this point in time, the evil Dark Elves are after the reality stone and would later kill Thor's mother, Frigga.
16. Events of Guardians of the Galaxy 2014:
The first Guardians opens with Peter Quill stealing the power stone, singing along to 'Come And Get Your Love' which we see from a hilarious outside persepctive in Endgame. Natasha even kicks one of those alien rat creatures just like Quill.
The villain of Guardians of the Galaxy was Ronan, who was ordered by Thanos to acquire the power stone. Here, we get to see Thanos ordering his daughters to join Ronan in the hunt for the stone. (Of course, time travel changes these events so that this Thanos travels to the future to kill the Avengers).
Nebula and Rhodey share a little moment about being partially cybernetic since Rhodey was paralysed as a result of the events of Captain America: Civil War and can only walk with cybernetic help or in the War Machine suit. Nebula is an android because Thanos would remove a body part from her every time she lost a fight against Gamora.
17. New Jersey in the 1970s:
This military camp, Camp Lehigh, visited by Tony and Steve was first seen in Captain America The First Avenger, where skinny Steve was trained in the 1940s and met Peggy Carter. In the next film, Winter Soldier, Black Widow and Steve return to the camp where they find out about Hydra growing inside of SHIELD, which is why Steve knows that the spy organisation is hidden in the military bunker.
This is apparently where they kept the Tesseract for a while, since SHIELD has possessed it since the 1940s when Howard Stark found it in the ocean in Captain America 1 (honestly the history of the Tessaract in the MCU is WILD since it also shows up in Captain Marvel, but I'll leave that for now).
In the movie Ant-Man, we learn that Hank Pym, the original Ant-Man, worked at SHIELD along with Howard Stark and Peggy Carter, allowing Steve to steal some Pym particles.
Tony encounters his father, Howard Stark, played by John Slattery, who reprises his role from Iron Man 2, Ant-Man and Civil War. Tony's issues with his father were explored in Iron Man 2 and Civil War.
Also, Howard's driver is the original Jarvis on which Tony based his AI system on. How do I know this? Well, in a cool casting decision, the driver is played by James D'Arcy who potrayed Edwin Jarvis in the Agent Carter TV show (which is brilliant by the way!).
18. Vormir in 2014:
This applies to Infinity War too but the 'red cloak guy' who always explains the soul stone is the Red Skull, who was the main villain in Captain America First Avenger.
Natasha says that Hawkeye did not judge her on her worst mistakes, a reference to her backstory which she tells Loki in the first Avengers. She worked for the Russians and killed a lot of people, but Clint decided to give her a second chance and helped her enlist in SHIELD. For more on Black Widow, see the character arc section below!
(Back to the present- yay!)
19. Thor calls himself the strongest Avenger, a callback to Thor Ragnarok
20. Captain America lifting Mjolnir:
First of all, hell yeah! Second of all, Thor says 'I knew it' because Cap managed to budge the hammer slightly in Avengers: Age of Ultron. Why couldn't he lift it back then? Maybe because he did not want to hurt Thor's feelings or because he was keeping the fact that Bucky murdered Tony's parents a secret and was therefore not worthy yet. In any case, though a lot of people predicted it, this was one of the best moments of the film.
20. Broken shield:
Steve's shield breaking was foretold in Tony's vision in Avengers: Age of Ultron, which also hinted at the return of the Chitauri.
21. The shot of Captain America facing Thanos and his army alone loosely calls back to an iconic moment in the original comics. Though the original line itself is incredible, it would not fit with Thanos' new plan so I understood its exclusion.
22. 'On your left':
Before we get the moment of absolute glory, we hear Sam Wilson's voice over comms, a callback to the Winter Soldier, where Steve says the same thing.
23. Portals:
I...I can't.... it's everyone. We see the Wakandans, sorcerors, guardians, ravagers, Spider-Man, Wasp, Howard the duck, asgardians, Scarlet Witch, Pepper. Everyone is here. And it's incredible.
24. Avengers...Assemble! A comic book splash page come to life.
25. Peter Parker finally gets that hug that he thought he was going to get in Spider-Man: Homecoming.
26. The hilarious van horn is from the Ant-Man movies. Who would have thought such a throwaway gag would end up in the most epic MCU battle? (Also, how does Cap talk to Valkyrie btw?)
27. Wasp saying 'Cap' is an Ant-Man and the Wasp inside joke hence the smile between the two characters- Hope originally teased Scott for calling Steve, 'Cap'.
28. Clint passes Black Panther the gauntlet:
T'Challa knowing Clint's name is low key hilarious because of their brief exchange in Civil War where Clint introduces himself and Black Panther replies that he doesn't care.
29. 'Activate instant kill':
Yes, finally! Spider-Man Homecoming revealed that Tony programmed an 'instant kill' mode in Peter's suit and there did not seem to be a use for it...until now.
32 Cap calls Spidey 'Queens', which references their exchange in Civil War.
31. Captain Marvel's sash. Yes, I want to talk just about the presence of a sash. Because her entrance, her haircut and that sash nearly brought tears to my eyes. Lifted straight from the comics.
32. We hear a bit of Captain Marvel's theme, by Pinar Toprak, when she destroys the ship.
33. The music that plays when Tony goes for the Gauntlet is aptly the piece that played when he made his first sacrifice back in the first Avengers by going through the portal- it's called One Way Trip.
34. "I am Iron Man"- the line that ended the first Iron Man film is the line that ended...Iron Man. *sob*
35. Thanos dusting away is a reference to Voldemort- oh wait. Scrap that one.
36. Wait, did I miss something? There's something in my eye.
37. 'Proof that Tony Stark has a heart':
This harkens back all the way to the first Iron Man. It was a gift from Pepper to Tony after he tells her to get rid of his old arc reactor.
38. There's a lot of characters present at the funeral, but one you might have missed is Tye Simpkins, who played the kid, Harley, in Iron Man 3.
39. Cheeseburgers:
The line that broke so many hearts. Again, we go right back to the first Iron Man- cheeseburgers where the first thing Tony asked for after he escaped from the terrorists who kidnapped him. Aptly, his friend, Happy Hogan, is played by Jon Favreau, the director of the first Iron Man.
40. 'How can you, you're taking all the stupid with you':
A line from Captain America: The First Avenger said by Steve when Bucky is going off to war, this time reversed.
41. In the comics, both Bucky and Sam have taken on the mantle of Captain America, but Steve chooses to give it to Sam in the MCU.
42. And finally, the song that plays during Peggy and Steve's long overdue dance- which Steve promised to Peggy Carter right before he went in the ice- also plays during Winter Soldier, when Fury breaks into Steve's apartment.
Character arcs
STEVE ROGERS
The First Avenger: "I'm going to need a rain check on that dance."
Age of Ultron: "God's righteous man, pretending you can live without a war."
Age of Ultron: "Family, stability. The guy who wanted all that went in the ice seventy-five years ago."
On one hand, Steve Roger's arc has been about moving on from the past- Winter Soldier and Civil War destroyed his faith in the government and also explored his inability to move on, something that is touched on in the post-snap world in Endgame. Steve's story ends with him living his life out in the past which seems, at first, to go against his development. However, looking back at Age of Ultron, we can see that the thing that really haunts him is that he has no purpose without a fight. His vision in Ultron had him reunite with Peggy, but still unable to let the war go. In Endgame, we see that, having won the fight, he allows himself to do the 'selfish' thing and live his life- in essence a reversal of Tony's character arc.
NATASHA ROMANOFF
Avengers: "I've got red in my ledger, I'd like to wipe it out.
Avengers: "I got on SHIELD's radar in a bad way. Agent Barton was sent to kill me, he made a different call."
Winter Soldier: "When I first joined SHIELD, I thought I was going straight."
Going after Hawkeye/Ronan and giving him a second chance mirrors Hawkeye showing her mercy as explained in Avengers and also wipes the 'red out of her ledger', not that it needed wiping after all the heroic things she's done over the years. Her conversation with Steve in Winter Soldier revealed that Natasha always felt she hadn't made up for her past crimes.
TONY STARK
Age of Ultron: "Maybe I should take a page out of Barton's book- build Pepper a farm, hope nobody blows it up."
Avengers: "The only thing you really fight for is yourself. You're not the guy to make the sacrifice play, to lay down on a wire and let the other guy crawl over you."
Civil War: "I love you, Dad. I know you did the best you could. That's how I wished it happened."
Tony's issues with his father date all the way back to Iron Man 2, and was subsequently explored in Captain America: Civil War where he expresses regret at not telling his father that he loved him. Endgame wraps this up nicely when Tony encounters Howard in the 70s and is able to bond with him since he now has a daughter, Morgan, and finally thank him for everything. The major arc (reactor) that Iron Man has been on is one from selfish narcissist to a truly selfless hero. This arc played out in the first Avengers too but Endgame has Tony making the ultimate sacrifice play, making Captain America's line from Avengers 1 all the more devastating.
Thanks for reading this rather long article, I just had to write it because all these easter eggs and timey-wimey stuff was swirling around in my brain. If you want to read more about Marvel, you can check out some of the recommended posts below.
I do not own any of the images used in this blog post.