I'd say that maybe a difficulty progression should be put in, along with a day/night cycle. As well as new hazards:
Difficulty Level 0: Starting difficulty. A single shark. No other hazards. A high amount of ocean debris, but low chance of barrels. High chance of jumping fish.
Difficulty Level 1 (Day 15 to 30): Chance of rain with occasional thunder. The rain makes you cold. When your heat bar is spent you get hypothermia and start to shiver and move slower, as well your health slowly drains. You are protected from the rain by being underneath a roof. Lightning can destroy tiles which further encourages using roofs. Chance of an extra shark or two sticking around for a day. Lower chance of debris, but higher chance of barrels.
Difficulty Level 2 (Day 30+): Chance of heavy storms, which can flood the lower levels or destroy raft components that arent reinforced or protected by walls. Chance of high winds, which can dismantle/blow away some of the lighter components (ie: cooking stations) that arent protected by walls. Chance of shark invasion, where additional sharks show up and stay near the raft for an entire day which means that multiple sharks can attack your raft at once.
I'd also say that maybe the player can also engage in 'spear fishing'. If a shark attacks and you spear it, it'll stay away from your raft for an entire day and you can do spear fishing by diving under the water. Being in the water for too long causes you to become cold and catch hypothermia.
Regular fishing should have a fishing minigame implemented. With high catch rates on water with jumping fish.
Being cold (even halfway towards hypothermia) should cause your food bar to go down a bit faster.
Dry foods should increase your thirst a little bit and coconuts should decrease your thirst twice as much as water, as well as refill a tiny amount of hunger.
All growth rates on growables (seeds and trees) should be halved.
Being cold can be recovered from by eating soups or staying near a fire. You'll also slowly regenerate heat during day time.
Shift-clicking an item while the inventory is open will quickly transfer items in and out of your hotbar or chest if applicable.