Continuity mistake: When Bucky jumps on the hood of the bus to get back in, the Creeper flies from in front of the moon towards the bus causing all the kids to run away. Bucky can still be seen staying put on the hood when they run - however in the next shot of all the kids running you see him at the front of the pack which would have not been possible given that he didn't run right away.
Visible crew/equipment: When the farmer fires the hole puncher cannon at the Creeper the first time with the line attached, the screen changes to a higher view, from here you can see there are two lines attached to the cannon, but he only fired one. This would be for the crew to pull the truck around safely.
Continuity mistake: Just after the man says 'he looks dead to me' (he means the Creeper) he walks past the girl who holds the black guy sitting/laying on the ground. The black guy is buried deep in her arms and he holds his right arm half over his face and on her left elbow. His fellow 'pupils' walk to him. Next shot: his fellow pupils walk to him, but now his right arm is lower, exposing his face and his right hand is now at his chin instead of on her left elbow.
Continuity mistake: When Izzy finds the javelins on the bus, Bucky is the only person at the front of the bus (because he is trying to call on the radio). In the next shot Scotty appears out of nowhere at the front of the bus and yells, "Sticks. You want to hang around here so that you can poke at this thing with STICKS?" with Bucky standing right next to him.
Revealing mistake: When the Creeper has been harpooned, he flies in the air dragging the pick-up truck with him. The pick-up truck moves towards the back of the school bus. If you look carefully you can see that the cable attached between harpooned Creeper and pick-up truck at times hangs too loose to be able to pull the truck, so obviously the truck is moving on its own (with hidden mechanics, which you by the way can't see).