Choices

[glatt]

Giving this serious thought, water is the biggest issue on all the small islands I have been on. Fresh water either doesn't exist or is so nasty that a purifier or boiling would do nothing. The tarp would let you collect rain water and you need a pot to put it in. Matches to get a fire going to try to distill salt water out of the pot, onto the tarp and maybe drip into your mouth. The only realistic chance at survival is getting rescued and a mirror is best for that because it will work for years and over great distances and a flare gun will only work if somebody is looking already.