Regarding pets, I could see having a seagull land on the raft from time to time with something in its beak. You could feed it some fish and tell it to go collect something specific you're short on. Obviously, they couldn't carry a barrel but I could see them grabbing some scrap or seeds or a tin can. Yeah, that requires a bit more intelligence than is really realistic for a bird but this is a video game.
A parrot could be a fun animal companion. While it may not be helpful in terms of collecting stuff, it could squawk when the shark approaches or give you occasional hints.