I assume other people are out of the picture. My five items:
A 12-gauge pump shotgun
Several crates of bird and buckshot (wonder what seagulls taste like?)
Large, sharp knife (seriously, a knife is arguably the most valuable item for this kind of thing)
Anything to start a fire with, probably flint & tinder
Fishing rod
The reason for the shotgun & ammo is fairly obvious - hunting and possibly protection, depending on what lives on the island. The knife is also pretty obvious - to cut things with. It can be used to help make crude shelter and other valuable items. A firestarter would serve to provide warmth at night, heat for cooking, as well as light and even some degree of protection. The most basic possible was chosen since it won't run out of fuel (lighter) and doesn't vanish at the rate that matches do, and can work indefinitely. The fishing rod is also self-explanatory. It's for fishing.