Capture a sea turtle and skin it (requires a new item, a knife) and use the shell to capture clean water during rain. Yes, totally stolen from The Forest but seems to be applicable to this game. This would introduce a new tool (the knife), a new animal (turtle), a new way to get drinkable water (shell), and environmental effects (rain). The weather could be extended to more complicated things like storms, giant waves, etc. where the raft can be damaged.