The game is called "Raft" so throwing out potential ideas of it becoming an explorer and more survival
Weapons and Tools
Bow and Arrow - These are a classic when it comes to survival games
Spikes - which are to be built on foundation to fend off AI
Armor - For foundation and player
Upgrades
Weapon Upgrades
Armor Upgrades
Building Upgrades (i.e. Stone)
Bigger Cooking station
Bigger Water Purifier
Bigger Chest
AI
Swordfish - More aggressive than Shark that'll jump and attack you on the raft
Birds - Will come steal your food when cooking
Dolphin - Can feed him… he does nothing but looks cool and you can waste food on him
Seals - They hop on and waste space
Environment
Natural Disaster - Could do some random damage around raft
Hurricane
Tsunami
Rain - Oh cool… rain…
Snow - Floating ice that comes by and damages nets
Day system where each day gets harder