If you are are ever stuck somewhere (like in the 'secret beach') and need to wait until a certain time to get back to the cave (and to Skye) then always carry a spear with you.

It can be a really bad one, because it doesn't matter. If you go into spear-hunting mode, and not catch fish, the time will pass at the same rate, but your health, thirst, and hunger will stay the same (ditto with Skye).

You will need to go back into spear-hunting mode about every game hour (or every real-time minute) because the game will take you out of spear-hunting mode after a period of inactivity.