Let's I tell you about my ideas how to survive on an uninhatant island. Probaly the 1st important thing is to switch the phone to energy saving mode or to turn of the phone. Secondly I would start looking for other alive people cause if I find anybody it will be more easy to survive together. Also this is a solution how not to go crazy.
In the wild insects can be really dangerous. And I can be bitten when I sleep. So, not bad option to protect myself is a fire near my habitat because insects don't like smoke.
About fire. Once I saw that wild people use a special fire bow. This is a stick with a stretched rope that hugs drill bit that rests on some kind of wood or on another flammable material. So, when I start moving this bow i will get a fire.
In case of having waterfall I would just use it to drink. If no waterfall or fresh water I would rely only on the rain. As for food I would try to fish in the ocean but how, I don't know.
In conclusion, I would like to say that in this situation is very difficult not to go crazy if you are alone. And even ball or stone with painted face will never replace human's conversation. So, it is really good to have some skills to survive.