I think that there should be enemies like pirates or whales and you can raid pirates ships and they could try to raid you. Flintlocks, Cannons etc. should be added to give an extra use for scrap and add gunpowder. There should be beds and the sleep requirement as well as heat and dealing with your raft getting caught on fire. There should be doors to protect you from enemies such as pirates and nails should be added so you can choose between rope or nails for your buildings. You should be able to reinforce your foundations and walls with scrap so that the shark cannot break it so easily. Here is a list of animals and enemies and foods that should be added:
More fish types just to add more variety into the game (Cod, Salmon, Tuna etc.)
More plants (Corn, maize, wheat, sugar cane etc.) for making different foods using a new object.
Foods you can make: Tortillas, popcorn, Bread, sugar etc.
Food Recipes: Tortilla + any meat or fish = Taco, Water + Sugar + Any fruit = Juice, Flour (Wheat, corn or maize) + sugar + Coconut milk + eggs = Cake etc. Be creative with foods as I think there is an entire range of food items that should be able to be crafted
Whales (Little bigger than a killer whale) That are rare but can destroy large chunks of your raft (Should only spawn after < 1 hour of playing) They should produce whale meat which should be a little more nutritious than shark meat.
Pirates. They come in a pirate ship and are armed with flintlocks. Their ship has cannons and can shoot your raft which will destroy whatever it hits. They have cutlasses and will board your raft and attack you. When you destroy their ship it drops loot (planks rope nails barrels scrap food etc.) and it all floats along for you to catch. Pirates can also loot any chests not behind closed doors but the cannons can shoot down the door
Birds. Birds can steal your food and create nests on your trees. You can harvest these eggs to either get more birds for food or for eating. You should be able to boil the egg in a tin can full of water over the cooking station.
Salt. Salt should be obtained by putting salt water in the cooking station instead of the water purifier. It should be used to make food more filling but take away from thirst
Finally the weird one. You should have the option to pee in a cup and drink it immediately if you are about to die and your water is still cooking. You should receive debufs for this like walking slower because you are feeling sick and you may have to vomit into the sea which will contaminate any water got from it for 5 mins.
Thanks for reading and I will come up with more ideas at a later date.