I think I will choose

+ water bottle: Around the sea, I can't find fresh water, so I need water bottle.

+ first aid kit: Perhaps I will sick, so I need first aid kit.

+ lighter: I need fire to cook food, so I need lighter.

+ fishing rod: I need food anh my food is fish, so I need fishing rod

And for greater certainty, I will write " SOS " on the desert island.