You could add a limit number of uses to an item, so it eventualy breacks.
Starting without a hook so we must swim to colect things at first.
Day-nigth cicle.
rainy weather.
fish net
food getting spoiled
other dangers apart of the shark (or more sharks).
Some kind of building, like spikes, to protect the raft.
may be an anchor that alows as to dive and colect things at depths.
sorry for my english :)