Audio problem: As Gilligan is carrying Kona, there is an earthquake and coconuts fall on him. However there is the sound of eight hits, but only four hit him. Also, there's the sound of a hit, but there's no coconut near him.
Continuity mistake: After the earthquake the skipper is holding the idol with both hands. The shot changes and only one hand is holding the idol.
Revealing mistake: As the gale force wind lifts Gilligan, you can see the outline of the harness under his clothes and can make out the wires holding him up.
Answer: Bob Denver answered this when he was on a talk show hosted by Pat Sajak. He said they were going to write into an episode where the castaways found all these clothes, but it got too complicated, so he said, they decided, "who cares, it's only a TV show," and forgot about it. So the writers and actors even asked this, they just never bothered to address it.