Continuity mistake: When the two teenagers find the axe in the bed, the axe is perfectly clean despite the fact it had been shoved through a girl's head. Furthermore, it also looks brand new with a fresh coat of polish on it as well.
Deliberate mistake: When they are playing strip monopoly, Alice purchases Baltic Avenue and then Bill rolls the dice and Alice exclaims that he's rolled an "8" - putting him on Baltic Avenue. However if you look carefully at the dice (before Brenda quickly scoops them up) you can see they show two 5's.
Plot hole: When the truck driver drops off Annie, she starts walking down the road towards Crystal Lake. Yet we see the others in the red pickup drive down that same road and Annie is nowhere to be seen. It just happens to be Mrs Voorhees who picks her up.
Plot hole: Assuming that the shells for the shotguns were kept in the locked drawer, why didn't Alice just go ahead and try to break it open? She had the time to do it with Pamela being knocked out so why not go ahead and have the gun loaded just in case?