1. In Iron Man 2, Tony Stark is seen standing in front of a map of Africa pinpointing the location of Wakanda.
2. In Spider-Man: Homecoming, a photo of Bruce Banner is among the posters of famous scientists hanging in Peter Parker's classroom.
3. In The Avengers, you can spy "A113" as a file name. This is a nod to the CalArts animation classroom where many Pixar animators studied.
4. The contents of Steve Rogers' notebook in Captain America: Winter Soldier are different in international versions of the movie.
5. In The Avengers, after the big fight sequence. the letters on Stark Towers are all missing except for the "A" — a clear nod to it later becoming Avengers Tower.
6. Also in The Avengers, Tony has blueprints for the Avengers Tower, complete with designs for their individual rooms, including Thor's, Hawkeye's, Captain America's, and his own.
7. In Guardians of the Galaxy, you can see that Peter has a "translator implant" as an enhancement. This allows him to understand various intergalactic languages.
8. In The Avengers, during the big fight sequence, you can spot the Shawarma Palace that the Avengers later eat at in the now iconic post-credits scene.
9. In Spider-Man: Homecoming, Michelle is seen reading Of Human Bondage, a book about an orphan boy who is sent to live with his aunt and uncle.
10. In Captain America: Civil War, you can spot the Bluth stair car from Arrested Development. The Russo brothers, who directed Civil War, also worked on the series.
11. In Captain America: Winter Soldier, Nick Fury's grave includes the fake bible verse from Ezekiel 25:17. The line was also quoted by Samuel L. Jackson’s character in Pulp Fiction.
12. In Avengers: Age of Ultron, the statues adoring the clock outside Grand Central Terminal have been changed to honor the first responders from The Battle of New York in Avengers.
13. In Iron Man, you can see Captain America's shield just behind Tony Stark when Pepper Pots is helping him get out of his destroyed suit.
14. In Spider-Man: Homecoming, Aunt May's license plate reads "AMF-1562." This is a reference to the first appearance of Spider-Man in the comic Amazing Fantasy 15, which was released in 1962.
15. In Guardians of the Galaxy, the stripes on each of the prisoners' legs correspond to a crime they've committed, while the pattern explains the severity of each.
16. In Captain America: Civil War, you can see that the only marks on Steve's shield are from Black Panther because both the shield and his claws are made of vibranium.
17. In Spider-Man: Homecoming, the URL of the video that Peter watches matches the URL of a Spider-Man: Homecoming trailer.
18. In Guardians of the Galaxy Vol. 2, Ego's car has the same color scheme as his son Peter's spaceship.
19. In Thor, you can spy Walter Simonson sitting next to Sif. Simonson famously wrote (and often illustrated) Thor comic books from 1983–1987.
20. In The Avengers, Tony Stark wears a Black Sabbath t-shirt, a nod to the band that sings the song "Iron Man."
21. And finally, in Spider-Man: Homecoming, Peter's phone screen gets more and more damaged after each battle.
