Continuity mistake: At the beginning of the movie, when Clark says he's not falling for the salesman tricks, Clark and Rusty start to walk back to their old car. Before the next shot, you can see Rusty walk past the back of the car and almost make the turn to the passenger side of the car. In the next shot, you see Clark trying to open the door while Rusty just starts walking up to the driver side of the car.
Continuity mistake: When Christy Brinkley appears in the Ferrari and Beverly D'Angelo is asleep in the car, Beverly's head is facing towards Chevy Chase. When they go to a shot of Chevy, Beverly's head is facing the other way. This continues back and forth throughout the entire scene, although she moves some.
Continuity mistake: During the campsite scene, the kids take the dog up to see the pool, the scene after has Clarke and Ellen finding their cabins. In the background, you can see the pool with the kids standing there, but the dog is gone. You can see there is no dog when they start to walk down the stairs.
Continuity mistake: When Christie Brinkley first drives alongside the Griswold car, the speedometer on their car is shown hitting 75. But when we see Christie's point of view of the car, it's clear from the trees in the background that the car is going about 35 mph. (00:26:10)
Continuity mistake: When they are on the looping roller coaster, they come to a point where it is a long drop in to the loop. However, in the next shots of Clark and the security guard, the coaster is going round a curve, and in the next shot it is back on the straight drop.
Continuity mistake: When the family finally makes it to Wally World, they park at the back of the lot with the car facing the park. As they pull up the shadow of the car is on the passenger side (right side), however only moments later as the family is running toward the entrance their shadows are on their left. If you look closely you can see that they are running from the front of the car, and the shadows should still be to the right.