Some ideas: Add fuel to cooking stations/water purifiers. a mode where you start on a lifeboat with resources, but floating debris is much rarer. Tools should lose durability. More sharks. More marine life - Turtles are known to approach lifeboats, fish should be seen swimming to the fishing rod. Fishing rod needs bait. Grab fish by hand if you're fast enough. Storms. Bail water out or capsize. Waves damage raft. Sharks rarely attack, unless they get hungry enough. Getting any kind of damage triggers an attack (they smell the blood), unless they have very recently eaten. After eating any food they come across, like fishes or food dropped in the water, some of the sharks leave. Food poisoning is likely if eating raw foods. Eating makes you lose water - more water is lost to digest the food than the amount of water you get from eating it. Islands to explore. You can use paddles to move the raft around, and the water flow pushes you around anyway. Make a knife, used to prepare food, a weapon against smaller creatures, cut rope.
Bugs and stuff that isn't right: can't find a way to remove cooking stations or water purifiers. Trees look really weird when they are small - They should be saplings, not really really small trees. Unclear when tree is fully grown. No way to store items. Debris is way to common, although I suppose there is no other way to get items.
Whew, that was a mouthful. Great game, though!