Audio/visual unsynchronized: When Marshall says "Cut it out you guys" to his brothers, his mouth does not move.
Crew or equipment visible: In the cave, one of the snakes is clearly a fake one on a stick.
Continuity: Marshall uses his brothers' toothbrushes (the green and yellow ones) to clean the toilet, then places them back in the holders with their names on them. Marty's is yellow, Mark's is green and Marshall's is blue. Later that night, Marty is using the blue toothbrush, Mark is using the dirty green, and Marshall is using the dirty yellow one.
Continuity: When the boys are going back to the cave after Mark has broken his leg, he is using one crutch and on the wrong leg. He is using it to support the leg without the cast, and putting full pressure on the cast. Later he switches the crutch to the other side.
Audio/visual unsynchronized: When the boys are in the home after Mark breaks his leg, the woman holding the child says "You'll bunk here, don't want to be eaten by a bear". But you can see she finishes talking before the words end.
Continuity: The scene where Marshall and Mark are in the swamp, Marty is clearly seen not filming them being chased by the alligator but later on in the movie, when they show their film they show the alligator chasing Mark and Marshall.
Miscellaneous: When the Dad crashes his big rig truck, the shot inside the cab reveals a woman to his right with a lit cigarette in her hand. She grabs him on the right shoulder and then he swerves to the left. Don't know if she is giving him a cue to swerve or she is the "hidden" girlfriend. We never see her again though!