*In the scare simulation at the start of the film, the toy plane from Toy Story (1995) is on top of the shelf.
*This one is REALLY trivial. On the simulation control panel are the digits ‘510-752-3000’, which is the phone number for Pixar Studios.
*On the scarefloor, Randall warms up by trying out his camouflage skills against different backgrounds, one of which is Andy’s wallpaper from Toy Story.
*Many of the names on the scareboard are those of Pixar employees, such as story artist (Joe) Ranft and story supervisor and voice of Roz (Bob) Peterson.
*When the blue monster George runs out the door because a kid almost touched him, there is a Paul Bunyan poster in the room. This was also in Sid’s room in Toy Story, the implication being Sid is the child who almost touched him.
*At the Harryhausen’s sushi bar (a reference to stop motion animation godfather Ray Harryhausen) a painting of Nemo’s father Marlin adorns the wall behind the chef.
*In Mike’s apartment, Boo removes a CD from his collection which has A Bug's Life (1998) written on it. This was a private joke for the Pixar staff and as such is virtually impossible to discern from this image.
*I’m not 100% sure about this, but supposedly when Boo is in the toilet she is singing to the tune of ‘One Love’ from Snow White and the Seven Dwarfs (1937) and the title song from Beauty and the Beast (1991). It appears around the 5:35 mark on this clip.
*Here’s another really trivial one. The cube of garbage which Sulley believes to contain Boo makes a squeaking sound which is taken from the Luxo lamp in the Pixar logo. Check out the 5.20 mark on this clip.
*The room into which Randall is thrown near the end of the film features Nemo on the wall.
*That’s not the only in-joke in this scene; the room into which Randall is thrown is actually the trailer from A Bug’s Life with the Pizza Planet truck parked beside it.
*Towards the end of the film as Mike takes Sulley to see Boo again, the Roly Poly clown from Toy Story is in the background of the scarefloor.
*Boo has a bunch of toys strewn around her room, including a Jessie doll from Toy Story 2 (1999), the Luxo ball and a Nemo toy.
*Rex from Toy Story appears as a very un-scary monster during the outtakes.