During the pre-crash scenes of the Mustang's windshield, the driver's windshield wiper changes both in type (factory and aftermarket) and color (silver v. black), switching back-and-forth in quick succession.
The goof items below may give away important plot points.
After Scott is killed, Chris, Jesse, and Carly are in the mountain men's truck, but they get it stuck in the mud and it won't budge. Throughout the rest of the film, the mountain men are on foot or have stolen another vehicle (i.e. the state trooper's car). However, in the end scene, when Chris blows up the mountain men's cabin, we can see the truck sitting there, and Chris and Jesse steal the truck in the end, without any hint of evidence that the truck had been moved from its remote location stuck in the woods.
When the trooper is shot in the eye and the cannibal throws him into the van, we see the cannibal throw his quiver of arrows in to the back of the van. After arriving back at the shack the cannibal drags the policeman to the hut we see him wearing his quiver of arrows without actually having picked them up from the backs seat of the car.
After the park ranger is shot in the eye and the cannibal picks him up we can see the arrow protruding from the back of his head. When the body is dropped on the road behind the cannibal's car and when the body is dumped into the car the arrow cannot be seen. Additionally, when viewed from the side window, the front of the park ranger's face can be seen. There is blood but no arrow.
When the cannibals set fire to the watch tower, Chris, Jesse, and Carly escape the flames by jumping down into a nearby tree. They haven't jumped very far. However, once they are in the tree, there is no recognition of a fire going on twenty feet above them. Large fires are typically able to be noticed from certain distances. So, in reality, there should be a bright orange glow, smoke, and noise, evidence of the watch tower that is burning to the ground nearby.