Many of the continuity "mistakes" were included intentionally by the filmmakers and were meant to be subtle and funny, including Neil's hair in the motorcycle chase scene and the differing level of completion of the blanket that Nancy is knitting when she gives Beth and Henry the library advice.
The van used to ditch the problematic campers in the woods is the same van simultaneously driving campers to the rafting trip.
When Beth makes Andy pick up his food, Andy's cup still has some juice in it, and he doesn't knock it off the table. When he starts picking up dishes, the empty cup is on the floor.
The raft on top of the van that Victor is driving to Moose river disappears and reappears.
When Coop finds Katie talking with her boyfriend in his cabin, Coop talks with her while standing in the cabin doorway. Shots of Coop framed by the doorway show that it is raining outside, but it is not raining before or after.
The zip code Henry gives Beth for Augusta, ME (04139) is not the zip code for Augusta - it's not a zip code at all.
After the town visit, the van is shown driving to the rafting trip on a 2-lane road. A sign on the shoulder of the road says "Interstate 95 Maine". I-95 is a multi-lane limited access divided highway, not a 2-lane surface road.
Coop talks about the Style Council (Paul Weller's band after the Jam broke up). The movie takes place in 1981, but the Jam didn't break up until 1982 and the Style Council didn't form until 1983.
On the "town trip" montage, the characters are seen eating French fries from McDonald's Super-Size fry containers. In 1981, when the movie was set, there were no Super-Sizes available at McDonald's.
Cure Girl's shirt has a still from the video for the song Love Song, which is on Disintegration. Disintegration was released in 1989, the movie takes place in 1981.
During the baseball speech, one of the campers is wearing a New Jersey Nets hat. The logo on his hat wasn't adopted until the 1990-1991 season, while the film is set in 1981.
The elastic on the men's Fruit of the Loom Briefs had the brand name printed on them which did not happen until years later. At that time the film was set, it was just the blue and yellow stripes.
Actors mark (a taped "X") visible when Beth demands that Andy pick up the food that he has thrown on the floor.
Cameraman's hand is briefly visible when Beth and Neil run into the back room of the infirmary.
When Neil is rafting down river with the campers, as he gets out of the raft, a cable can be seen attached to the back of the raft.
Reflected in Neil's sunglasses, after stopping his motorcycle on a haystack.
When Victor and Neil arrive at the campsite, Neil opens the front door of the van and you can see the camera assistant's reflection.
When Henry is demonstrating the Earth revolving around the sun, he says the Earth makes a 1.3 million mile trip every year. Actually it is more like 585 million miles.