Other mistake: When Hilts and Ives are taken down to the cooler for the very first time, just after arriving at the camp, watch the wall as the door is closed by the guard behind Ives - it very obviously moves as the door slams shut.
Other mistake: Take a look at the size of the rock that the boys push onto Piggy. A rock of that size, falling from that height would've exploded Piggy's head like a ripe melon. It also would've crushed his body into a mangled heap.
Other mistake: In the scene in which two Japanese Zero fighters bomb and strafe a PT base, shots of the attacking planes show them carrying no bombs. During the attack, they still drop around 20 bombs anyway, which is considerably more than the actual carrying capacity of the two planes.
Other mistake: When Elizabeth (Catherine Bell) gives Merrick (Casper van Dien) the note with her phone number, we see that the number is 555-1234. But when he calls her, the number is 555-0199. (00:08:46)