Revealing mistake: Allison is wounded by a grenade fragment while disabling the Japanese 105's. But when his bloody shoulder is first seen, the blood stain is visibly too bright for real blood.
Continuity mistake: When Allison arrives at the island in his raft, he sticks out his head to take a look. When his face is seen, his hair is completely dry, but when his back is seen as he prepares to go ashore, his hair is soaked.