I want more info about this island. Is it deserted? Are there plants? Fresh water source (spring, etc) or no? Assuming there are and it's like a Swiss Family Robinson-kind of island:
Like Elo said, a machete for sure. Extremely useful.
Honestly I'm not sure what else. If this island is like the Robsinsons, then you can get everything you need from it directly. Yeah mates: didn't think of that, did ye?
*Bows*
Ask me anything.