I would include day an night, so during the day you can get burn and you hace to craft clothes to protect you. In the night you can see iluminated animals in the water.
Also that you can craft rafts to explore other islands, and there you can find new materials and enemyes.
I wish there were traps for sharks, archery, lances of differents materials, when something collapses the animation appears, and that when te shark is about to attack you appears the song of the shark.
Pirates!! I would like to include pirates, good pirates and bad pirates.That would be awesome!!
If there is day an night you can include lightning, like torches. Electricity of the water courses, that is great, you can cook faster and have ilumination whith lapms. Rails and wagons for a faster transport. Armor to fight.
Those are all my ideas. Only one more for the end of the game...
When you passed the game, that a helicopter comes to rescue you.
That's all, I hope you put some of my ideas. Bye!