Add animals you can tame such as seals and small squids. The seals and squid would be tamed with fish. The animals would have an ability. The squid would be able to bring resources from the ocean floor the more squids you have the bigger items you can get. Squid would be able to bring small clumps of sand, scrap metal, rock, coral and other junk. Seals would be able to defend the raft and hunt tuna for you the player to eat.
Also allow the player to get palm oil from palm seeds for something.(I always have a chest full of palm seeds)