Heres some suggestions that you can add to raft:
day & night cycle
Bed - to sleep at night
chest - to store stuff in
more then one type of fish (When you fishing)
a way to trap the shark
new weapons to defend yourself
multyplayer (it will give the game a bigger fan base)
settings - add an option to change the graphigs for low budget computers
add end scene to the game (you found an island/some one came to rescue)
Thank you for reading this and i hope you will add some of thos ideas :) .