Ken's first night in Vegas, he goes to a little burger stand, in one shot the cup on the tray is upright, then, in the next shot, it is knocked over and finally, it becomes upright once again.
When Kenny is on the bike chasing the Corvette by hitching the RV, you can see the red tail light of the RV first, then you see it broken, then you see it unbroken again for multiple times.
During the chase of the gold-colored Corvette by Kenny on a bicycle, they go through the same intersection twice - once when he lets go of the motor home when it turns, and again when he goes to grab onto the blue pickup truck.
When Ken and Vanessa flee from Vegas toward the end of the film, Vanessa is wearing a red and black wetsuit. But during some shots during the chase scene, she appears to be wearing a different outfit. This is noticeable when they're in the quarry. When Ken first stops, she's wearing the second top (which looks kind of like a Starfleet uniform top from Star Trek), but then when she pokes her head up out of the car a few seconds, she's got the wetsuit on again.
In the car chase at the end, both cars are almost completely covered with dust. When shown from overhead, they are sparkling clean.
In the beginning of the movie, the emblem that falls to the ground and gets Kenny's attention says "Corvette" - this is a script from a 1963-1967 Corvette Sting Ray rear deck. It should say "Stingray" if it had fallen off a 1973 Corvette Stingray.
When Ken is chasing the Vette on a bicycle, he hitches boosts in speeds by holding on to various cars along the way. At one point, a construction pickup is one of these "boosts." The driver had to honk and actually slow down for the stuntman on the bike to catch up and grab hold.
Several scenes where actors have been clearly replaced by stunt people in particularly bad wigs.
When Kenny tries to escape the storeroom after being captured by Wayne and his gang, he breaks a window which attracts Wayne's henchman. The henchman sees a "ladder" of crates, paint cans, and other things on top of an oil drum leading up to the window, believing Kenny climbed up them to get out . When he leaves, Kenny emerges from inside the drum.
The high school teacher congratulates students for studying, claiming most of them ended up on plus side of "bell curve" following recent test; but there is no way a majority of them could wind up either side (plus or minus) because a bell curve is a graphic way of demonstrating the norm (in this case, test scores) in the middle, with upper or lower scores trailing off equally on either side - hence the "bell" designation.
When Kenny is on the bike and hitches the ride on RV to catch up to his Corvette, you can see a street sign that says Van Nuys Blvd. They were still supposed to be in Vegas at that part of the movie.
At the gas station in Las Vegas we see a 1978 vintage RTD (Los Angeles) city bus pass in the background. And during two other chase scenes two other RTD buses can be seen along the city street.