I think the shark should go away sometimes, so you can swim in peace.
Underwater walls and floors etc for pools.
Door walls, self explanatory.
Deep sea diving, to find more materials.
Taming sharks, to have a way to get around.
Bird traps, made from: Scrap, Rope, Balloon(s), and wood, it would be a spool with rope and a cage at the top to catch birds (that you can reel in once you've caught a bird).
More advanced tech, like an automatic water filter.
Having the Raft pass Islands.
Fishing Nets.
Actual fish, not just items.
More food, get eggs from barrels, like potatoes you can either cook them right then, or wait and have more food, Yay Chicken!
Getting rations from barrels.
and that's all i got.