42

42
The number 42 is consistently included in many, if not all, of Pixar's films.

Possible Explanations
One possible explanation can be a fascination with Douglas Adam's Hitchhiker's Guide to the Galaxy ; this is just one assumption.

Finding Nemo
It is found in the address of the dentist: 42 Wallaby Way, Sydney, Australia.

The Incredibles
It is found in the first droids screen while trying to kill Bob Parr (Mr. Incredible) inside the volcano.

Cars
Lightning McQueen says 42 while stating how many cars are on the track in the introduction.

Wall-E
Before realizing he is late for the morning announcements, the Captain's screen reports 42 before immediately turning to 43.