What an awesome game!! There's so many replies to dig through - so I'm guessing most of my suggestions would already have been said somewhere in the gigantic pile, I tried going through a reasonable number so apologies if this is just a repeat.
I love the idea, and without adding too many intricacies, some ideas for the future might be:
1. Setting up a basic background - like some small green islands on the horizon, perhaps only parallel to your journey direction so you're not travelling to somewhere per say. Whether it's continuous hill shapes, or the odd bare sea to make it 'look' like your travelling is up to you (unless the idea is that you're in the middle of the ocean with absolutely NO land in sight). In which case never mind!
2. Along with that basic background, if you're into that kind of thing, could be setting up weather climates. Such that desert looking islands (yellowish in the distance) may give incentive to create a roof to your raft to shelter you from the sun or you lose water much too quickly without it. And whiteish land in the distance could mean ice/snow, so important to not be too far away from a 'heat source' like a torch/food cooker that kinda thing, or else you may lose hunger too quickly.
I guess along with that you could introduce different types of materials found in said climates. i guess it just adds a bit of variation to it all, like different fish or even using seals instead of sharks or ice covered barrels etc.
3. Multiplayer was awesome! Being able to share chests and such in the future would be amazing, and brings a bit of an added challenge when sharing the food cookers and such.
4. Beds or sleeping through the night would be neat, I guess it may fit in more if there was more consequences at night like more shark attacks etc. Day/Night cycles are excellent though!
5. Would be great to perhaps slightly increase the range/distance certain items appear. Such as making rarer items appear and last longer on screen giving the player incentive to build their way out there to collect it, whether on temporary cheap platforms (break after a day/night cycle for example) or on regular ones.
6. Ranged weapons could be thought about if there's the ideas of adding in more enemies that might attack at different times and do more than just eating one piece of the wooden platform (like shaking the raft and perhaps losing a few platforms in random places such that centrally placed items aren't 100% safe). Just motivates the player to want to get rid of the sharks rather than just letting them eat the outside pieces and not really caring too much when you have 50 around you.
Anyway, maybe a bit too much there, I'm sure it's all been mentioned before, but I really enjoyed it. I greatly look forward to seeing where it goes and contributing to it where I can.
All the best to your team!!