Other mistake: In the scene where Judy and Becca are strapped to beds in the high school and the principal is coming with a pitch fork, at first there is a close up of the fork (when the principal is dragging it) and its dry with no blood, the principal walks over to his first victim and right before he raises the fork it is shown covered in blood so much that some has ran on to the floor.
Continuity mistake: When the principal stabs the 3rd victim (male) on the gurney, we see that the tongs on the pitchfork extend almost their full length underneath the bed. However as we see up top, the pitchfork couldn't have been that deep given it had the height of the man's chest to go through as well.
Factual error: Given the destruction from the nuclear blast threw the truck in the air, the rest of the surrounding area would also have experienced similar destruction. However when they are walking away from the truck to another town in a nearby field, there is no visible impact of what was a recent nuclear explosion anywhere to be seen.
Continuity mistake: At the end when we zoom up from the Sheriff and his wife, the "spy satellite" view zooms significantly back but we don't see any of the telltale evidence of the recent massive explosion to the south of them that was seen in the distance while they were walking through the field.
Revealing mistake: At the end scene when the Sheriff is escaping in the truck away from the nuclear blast, the truck begins to flip through the air. While it is flipping we see under the vehicle and can see the hole they use to launch a post to help flip the vehicle for the stunt. A brief puff of white smoke also emanates from that hole briefly during the flip.