Zack's shirt in the outhouse scene goes from being covered in toilet waste, straight to a fresh shirt, and then back to soiled.
In the final scenes, the record with the country song, having reached the run-out grooves, changes labels between different shots.
At the end, the younger brother goes back and forth from missing teeth to have a full mouth of pearly whites.
In the "desolate" campground, at various times you can clearly see car lights passing. Noticed first while Rachel is searching for Zack but it is throughout the movie in many scenes.
When Pete and Bryan are in the tent discussing returning the stolen film, Bryan's mouth doesn't match what he's saying in the over-the-shoulder shot.