What you need to use for shelter
You could use caves.You need to make a tepee out of branches,then you need to cover it in foliage or other resources.You need to also use your surroundings to you advantages.Plus you could use trees for shelter.You could climb the tree so you have shelter and keeps you safe from predators.
What you will need to find things to cook and find food
A way you could cook your food you could use the Fire Plow Method.You need to gather soft wood and cut a groove in the wood.Get a stick and plow in side it to create friction.Then blow it so it will have best chance for it to catch on fire.The best way you would find food is to look for fish in the shallow ends.If there's no fish look for fruit.
Finding fresh water you can drink
You will need to get rain water.You can get rain water by making a solar water still.You can make one digging a hole in the sand.Then place a container in the center of the hole.Surround the container with wet leaves to fill in the gaps.Put a sheet over the hole.
How you will get off the island
A way to get off the island is to make a with stable branches.Get a lot of logs and inter wire them together.Another way is to write SOS with logs.Set them in a way a person in a helicopter so the can rescue you.Also make the letters BIG so its visible.
What do i do if i need first aid
You could use plants like if you get a sunburn you could use a aloe plant.Some fruits even help.Make sure its not something that will kill you.Specific plants help with specific kinds of injury's.Also you could find a plant to cover the injury.