It would be interesting if you had some "rare item drops" from barrels-- things that didn't occur too frequently and could be used to create special items, like more powerful weapons or unique furniture-type stuff. Maybe make it like something from whatever shipwreck seemingly left you stranded out there. Other animals would be interesting, too, even if they were just for ambiance. My suggestion would be to have an albatross that flies overhead, maybe lands on your raft for a little bit.