make it have little bit story like fall from ship or something like that
And also ad some mechanic
Example: u can make computer chip wrench Etc
And you also can make radio and something else to comicate to people
also item that can detect your coordinate so people can help like helicopter
I have another idea too like a Day time they use shark but at night the shark sleep
so u can explore under water too find some item
Example:seaweed ,soil (for tree i mean where the soil comefrom if not from under water),rocks,coral,Etc)