Add islands that you drift past but you can make an anchor to anchor your raft to on, get on land and collect resources etc. add new items on the islands like rocks etc. and new animals like boars of some sort
these were mentioned before but bows and arrows aswell as birds as something to shoot at, fire arrows that dont do much damage but scare the sharks enough to get them off in 1 shot, wooden, metal tipped, hook+rope arrows which act as a longer range version of the hook, roped arrows so you can reel in the birds you shoot down
more buildables like spiked platforms that deter sharks from that area, ad the ability to go diving and collect items off the ocean floor around islands, could salvage from wrecked ships etc. and get technology like wiring with a win condition if you make a radio
ability to reinforce platforms and pillars with metal if you want to build floors even higher but with limitation that depends on how large the base platform of the raft is, add a rudder and sails to steer your raft towards wrecks and islands and the ability to make smaller rafts so the main one can be anchored off shore and you take an exploration dingy to islands etc. this would be very useful with multiplayer, also add obstacles to avoid like rocks etc. that damage the raft a lot
and also multiplayer ^ and a difficulty system as 1 shark wont really be that threatening once you have a crossbow or something. a skill tree would be a nice addition and have to level up crafting before you can build anything too complicated, add strength which can increase inventory space and throwing distance, agility for speed and swimming, survival for better metabolism so foods last longer etc.