Continuity mistake: When Sam is swinging the shovel at Putnam's car he busts the driver's side headlight twice.
Continuity mistake: They get off a pickup truck after having hitched a ride. Then much later after having slept the night in a junkyard and hitched a ride with some motorcyclists they can be seen hitching a ride in the same pickup truck that dropped them off earlier in the film. (00:27:39 - 00:33:31)