Easter eggs are always something fun to look for, and Pixar never disappoints in that regard. They always have a number of easter eggs that you can rely on finding in every film. Viewing Cars 3 we found all the standard ones we expected, plus a couple of others that we were just as much fun.
The Luxo ball shows up in the very first short that Pixar chief John Lasseter ever created for the company, Luxo Jr. You'll recognize the lamp from the Pixar logo, but the ball also appears in every Pixar film. In Cars 3 it makes an appearance in a slightly different way. We never see the ball itself. Instead, we see a car during the demolition derby scene which has a paint job which matches the look of the ball. This is similar to the reference we got in Finding Dory, as the pattern of the ball was visible at one point, but we never actually saw the ball itself.
A 113 is a reference you see in a lot of animated films, not simply those from Pixar, it's a reference to the classroom at California Institute of the Arts where many animators learned character animation and graphic design. In Cars 3 this is probably the most obvious easter egg that's the hardest to miss. It's the office number for Nathan Fillion's Sterling and the number is right in the middle of the screen before Lightning goes in to speak with him. You have to work to miss that one.
Pizza Planet Truck
The Pizza Planet Delivery Truck is first used by Buzz and Woody in the original Toy Story, but since then it has appeared in nearly every Pixar movie. The truck has a rough time of it in Cars 3. Like the Luxo Ball, the Pizza Planet Truck can be found in the demolition derby scene. Things don't go well for him, as at one point he gets hit so hard that his rocket ship logo that's sitting on top of him gets knocked into the stands and grabbed by a fan. Needless to say, he doesn't win.
The final easter egg that you can be almost guaranteed to see in a Pixar movie is a reference to their next film. In this case, that film is the Day of the Dead story Coco. This easter egg is as prominent as A113, as long as you know you're looking at it. During the scene where we first meet Cruz Ramirez, she's training three other racers on treadmills. One of them, with a Mexican accent, requires motivation, and so he gets shown an image of his hometown on a monitor, if you've seen trailers for Coco you'll recognize it as the same town which the film's hero Miguel hails from. There's also a reference to the film's musical component with a shot of a guitar during the scene at the bar where Lightning meets the racing legends.
Buy N Large
There's a fantastic fan theory that all Pixar movies take place within the same universe and on the same timeline. This theory claims that the Cars movies all take place in a far future where all humans have left earth in the events that preceded Wall-E. Pixar would seem to be lending some tacit support to this idea when they included the fact that Buy N Large, the massive conglomerate that took over the Earth in those days, is actually a race sponsor in Cars 3 whose logo can be seen during at least one of the race sequences.
Not ever easter egg in Cars 3 is specifically a Pixar reference. There's at least one call out to a classic Disney film. During the sequence where Lightning meets with Sterling in his office, a miniature version of Cinderella's carriage can be seen on the shelf on the back wall. Check out the upper right-hand corner of the image above. Most of the shelves appear to be filled with awards so this could be a trophy of some kind. One would assume that in the Cars world this carriage is actually alive, so maybe it's the symbol for a classic car company or something.