Factual errors: Among the debris washed ashore after the shipwreck is an anchor.
Continuity: Haakon's footwear repairs itself as he spends time on the island. When he's washed ashore, he's barefoot, or nearly so, and when he falls into the pit he has just part of a shoe on his right foot. Then, as he builds the boobytraps, he has parts of shoes on both feet. He sees the flare from the other island, builds a boat and launches it barefoot - then wades out of the water on the other island wearing two completely intact shoes.
Revealing mistakes: When Haakon drops a crate with explosives in it onto a bonfire, it blows up before it reaches the bonfire.