I have many ideas, and I want to put them in a format that isn't overwhelmingly difficult to understand. BEFORE YOU READ: Please note that these are all suggestions from me as a fan, and that these aren't things I think should be done anytime soon! Everything stated in this post are long term goals, and aren't specifically described.
Tiers- Think of it like any ranking systems. For example, minecraft. You rank up your materials. Maybe it could be, in this game, that you combine wood to get "Tough wood", then combine that to get "Tougher wood". These upgraded supplies would hold up to the sharks loads better.
Or an alternate to this, as you play levels. I don't have loads of experience in unity, but I dont think a level system would be too terribly difficult to incorporate. This would mean, as you play you get xp for doing certain things, gathering materials, fishing, attackings sharks, building, etc. As you rank up higher tier loot starts to float in. You would also gain access to different crafting recipes. However ranking up would also makes things more difficult. More sharks spawn perhaps every 10 lvls, and they get stronger as well.
Food- I know this game is pre-alpha, so nothing is final but I have some suggestions for food. Fishing honestly shouldn't be as easy as it is in Raft, I'm sorry I have no suggestions how to fix this though. Food should also be available in more quantity, IE, different types of food and different ways to obtain it. For example spear fishing. In my opinion, there should be "water jugs", in which you could get 3 water cups worth of water in 3 different left clicks. Also, I was thinking you should spawn in with a bit of water and bread. This kind of makes sense due to the fact that you had to have something with you before you were lost at sea.
Enemies- short and simple, more sharks per lvls, and different types of them. Maybe a boss that appears every once in a while.
Inventory- The gui system as it is now, works however, it is not smooth. Some simple adjustments the inventory managment fontrols could solve this extremely easily. Ex. Shift clicking, right clicking to take 1 item of a stack, perhaps even change the stack limit to 25. One last thing to the gui, chests seem to not have a very high capacity, I see why this was done though.
Miscellaneous- Polish GFX, Polish Sounds, Polish launcher menu, Polish Shaders. Add third person views, add an "Options" tab in the menu and ESC menu to change sensitivity, graphics settings, and other random things.