You have a belt, a lighter, and a small pocket knife.
The island is identical to the one in Cast Away so there are trees, coconuts, and enough water to live on because of the constant storms.
THE CATCH: There is a tribe of semi intelligent and aggresive crab people, about 5 feet tall, that live on the far side of the island, in and around the cave from the movie. There are roughly two dozen crab people and from your limited observations, they seem to be lead by a large but old crab person who likes coconuts.
Describe, in detail, how you would approach the situation
I'll share my strategy after a few people respond