Hello, I'm enjoying raft very, very much and I think these ideas will hopefully make it even more enjoyable.
First of all, if you add a thing to catch fish automatically like adding a fishing net or have fish actively swimming in shallow water so you could attack them with your spear. Also make fishing harder, right now I think it is too easy to catch fish.
Okay, about when and if you add multiplayer make sure you that you make different types of multiplayer. For example, when you go to make multi-player make different modes so there could be a mode where you can socialize, make friends and help each other out without making other players able to attack you.
The other mode could be called Competitive. Where you can travel across the ocean to find other players rafts and raid them. Please do not make it able to team in competitive if you decide to add a teaming mode please make it separate.
Make the game harder. For example, make floats or something where you have to put them under you raft to hold up your raft and if you make a 10 floor raft like me for example please make it so you have to build a floating foundation underneath. If you decide to use that idea have a little menu when you open the crafting menu that tells you if you need more foundation or not.
Make a backstory. My mind honestly needs to know how your player got where he/she is
I think you should add a creative mode this could be single player and multi-player. In the single player mode, you should make it so you don't starve you don't take damage no sharks unlimited resources and remove thirst. For the multi-player you should do the same thing, but you can have your friends help you build the best raft.
Try to make it on steam! You could invite friends from your steam account to help you. Plus the steam workshop is a great way to download and play with rafts you find on the workshop.
I think your game is great and has a great future ahead of it. Keep it up!