Jim Hill has a fantastic post about the in-jokes and self-references that appear in Pixar's feature films and shorts. Take, for instance, this beat up Pizza Planet truck to the left. Turns out, the car has been in every single feature film that Pixar Animation Studio has produced to date:
It's the truck that Woody & Buzz stow away in when they're trying to hitch a ride to Pizza Planet in the original "Toy Story."
This is also the vehicle that Buzz "borrows" in "Toy Story 2," when that space ranger is trying to prevent Buzz, Jessie and Bullseye from being sent to that toy museum in Japan.
You can also catch a quick glimpse of the Pizza Planet truck as Gill is explaining his latest escape plan to the Tank Gang.
The Pizza Planet truck also makes an appearance in the Piston Cup sequence of "Cars." You'll find him to the far left in the photo below, next to the RV that looks like Elvis Presley.