12. In the camera shot where Elsa hands the Holy Grail to Donovan in Indiana Jones and the Last Crusade, you can see her shake her head subtly to Indy behind the grail to let him know it's fake.
14. In Polar Express, they used the director's childhood address for Billy's house, and the house itself is modeled after another house in the neighborhood.
19. Flash reads a BuzzFeed (nice) article in Spider-Man: Far From Home that claims "there's a sailor named Morris Bench who was exposed to an experimental underwater generator and got hydro powers," which is the origin story of Hydro-Man, a Spider-Man villain from the comics.
21. A blackboard in the movie Catch Me if You Can says, "Steven + Tom's 4th project," referencing the fact that it's Steven Spielberg and Tom Hanks's fourth time working together.
Technically, this is their fifth project together if you count every Spielberg-produced film and the miniseries Band of Brothers, but it seems likely that they're counting differently.
22. In the attic in National Lampoon's Christmas Vacation, there's an "It's a boy!" sign stuck between some beams from Rusty's birth.