Corrected entry: At one point in the movie, Gerry watches Josh shave and is fascinated by the fact that he has been shaving for years, but there's a problem: Josh is shaving wrong. When he shaves, he always brings the razor down. Most people would know that in order to have a nice, clean shave, you also have to go up.
Corrected entry: Near the end of the movie, they are having the Apache race. Normally in a relay race or any race you don't stop, but as you can see when they get to the cars even when the relay has reach them people crowd around and get ready, but really people go as soon as possible.
Correction: This was done deliberately to heighten the drama, everyone is obviously aware what really happens in a relay race, this isn't a mistake.
Corrected entry: When the campers are having a party after capturing the leader, food is flying everywhere. But when they wake up, you see that there is no food in their hair, just on their faces.
Correction: Watch the scene again, several campers have food everywhere, including their hair.
Correction: Character mistake if anything. Some people (like me) only shave down and can get a clean shave that way.