If the island is so dangerous that you need to provide survival caches for people, why not implement a permit system? Nobody is allowed to go there without an advance permit that details their plans, and informs them about resources on the island. For survival caches to work, you'd need to pre-inform people about their existence and locations in the first place. So just replace that pre-inform step with a permit system.

For people who would ignore the permit system, then they would be on their own, as they should be.