What would the sextant be for? If you're only a mile from an island, I would hope you would already have some idea where you are. Ditto the map.
What's the gasoline for? Can't see why you would need it. Ditto the rum -- pointless.
Shark powder? I doubt you've got a mile's worth!
Wrap all the other stuff (except the water) in the plastic and attach it to the flotation device, then push all toward the island.
Sue