Some casual props you could add:
-Ruby Slippers from the Wizard of Oz
-One Ring from the Lord of the Rings
-Blue and Red Pills from the Matrix
-Drinking Bird from Alien
-Can of Barbasol from Jurassic Park
-"Save the Clock Tower" Flyer from BTTF
Those are some of my favorites.
If you wanted to go all out, you could hang up "Rosebud" from Citizen Kane.