In Avengers: Endgame when Captain America is going off to return the stones, the rest are expecting him to return. Bucky says his goodbye knowing Steve is not returning to his timeline, a testament to their friendship.
2The Usual Suspects
In The Usual Suspects (1995) everyone is cracking up in the lineup scene because Benicio del Toro ripped a nasty fart. Director Bryan Singer left it in the movie because he thought it showed a camaraderie between the felons.
In Avengers Endgame, during the opening scene with Clint’s Family, many birds can be heard in the background. When his family vanishes, the sound of the birds goes too.
4What We Do in the Shadows
In the movie “What We Do in the Shadows (2014)”, in the chips scene none of the vampires have a reflection on the table.
In The Flintstones (1994), during the opening sequence, when the characters go see the drive-in movie, the “Univershell” logo shows the earth as Pangea.
6Iron Man 2
In Iron Man 2 when War Machines armor is compromised the language in the suit changes to Russian.
7Stranger than Fiction
In Stranger than Fiction (2006) when Harold is thinking of Ana during his visit to HR, the cloud painting behind him begins to move, indicating his head is in the clouds.
In X-Men Apocalypse, the woman that Stan Lee is holding in his arms is his real wife, Joan Lee. It's the scene in which Apocalypse uses his powers to launch all the world's nuclear weapons into space, essentially disarming the entire planet.
In Avengers: Endgame, in the support group scene, the man wearing the glasses is Jim Starlin aka the creator of Thanos from the Marvel comics.
10Spider-Man: Into the Spider-Verse
Seth Rogan has somewhat of a cameo appearance in Spider-Man: Into the Spider-Verse.