More weapons with different damage.
Crafting a small boat to arrive to far small islands with different loot.
SPECIAL BARRELS with special loot to make special craftings like bombs, guns, reinforze your raft with metal, etc.
Traps for the shark and fish.
craft a Underwater suit and well, go underwater to find loot.
A HISTORY, WHY HE IS THERE?
Bottled messages, that give you useful info, where is an island, tips for surviving, and some kind of ULTRA SPECIAL STUFF, like a Watch, or food that fills you a lot of hunger bar.
A faster (and expensive) way to cook and purify water faster.
and if i get more ideas, i will post them all here.
If i have any english fail, sorry, im spanish :D