Some thoughts after trying V1.04 some hours.
Looks like it could be a nice game. Just that as is it is very unrealistic, since any larger ocean/water have weather that creates different waves and situations. Coding a raft that moves with waves would be demanding though; Rain, wind, movement, lightning. Add some sense of movement.
Missing a goal to work against, like being rescued. Maybe now and then you get a part to a radio transmitter of some kind.
Or get parts to build signal rockets, to alert planes that passes by very seldom. Air drop option possible too.
Or build the raft to a certain size with stuff/farms. Anyway there ought to be a max size (3D).
Or survive for a certain time, then have to add some hazards along the way. Difficulty could be added by larger debris that can hit the raft and destroy parts.
Canned food and glass jars could also be found in barrels. Option for multiple uses for such items.
Small reefs and islands too could be added. For possible damage to the raft and/or getting special resources, food or materials or whatever.
Some debris could be (large) parts of other rafts or boats, with the ability to salvage stuff. Maybe have to create a long rope to tie to you and your raft. So when time out you get pulled away.
Not sure if should add the possibility to dive (and swim better). Making equipment for diving and catching.
If to add pets then islands and larger debris could contain cats, dogs, chickens, lizards, crabs, and so on.