After Alison gets in the truck, the view from behind shows the barrels next to each other, touching. The next shot from the front of the truck shows a gap between the barrels.
When Gib teaches Alison to shotgun a beer, his pants become soaked with beer, but when he leaves the room they are completely dry.
When Gary is driving after the first night in the hotel he is on the left-hand side of the road. In the next shot he is back on the right.
The color of the car they are traveling in.
Preparing for his study date with Alison, Gib tucks his shirt in twice.
Gib takes a bite out of pink Sno-Ball snack cake while riding in the car. The film is supposed to be set during the Christmas Break. In 1985, pink Sno-Balls were only available during Valentine's Day.
The trees and the grass are too green in the Midwest for a trip that is supposed to take place in the middle of winter.
Early on in the car trip, a shot shows the car moving from screen right to screen left, coming at the viewer. However, the car appears to be driving on the left hand side of the yellow line in the road (driver's left), obviously a shot flipped in post production/editing.
While in the blue car they are supposed to be driving west to California yet at the end of the first day there is a shot of the car coming toward the camera with the sun setting behind it which means the car was driving east.
During the swimming pool scene, as the camera pans following Alison swim, the upper right hand window reveals the top of a palm tree. Very odd for the New England setting.
Walter attempts to placate musical theatre fans Gary and Mary Ann by singing the song "Feelings" by Morris Albert. "Feelings" is a pop standard and is not from any stage musical.
Alison mentions crying when she saw Elvis Presley's bedroom at Graceland. The upstairs of Graceland, including his bedroom, is off limits to visitors.
When asked by his roommate how to spell "zucchini," Gib spells it "zuchini," missing a c.
When Walter winds up in the bar out of frustration with Alison he orders a double shot with a beer chaser, and eventually buys rounds for the whole bar. However it's already been established that he has no money.