Basically what I'm doing now because I'm already on one. It's freaking HUGE this "island" that I'm on. So huge in fact it is often called a continent not an island, but looking at a globe, I noticed that if I follow the entire coastline this thing I'm living on is surrounded by water on all sides--An island! Creative enough for you?
I would spell lost with some rocks. I would find two twigs to make a fire. Get a bowl-like object to put some water in and boil the water so it will be clean. Then drink the water. I would eat some coconuts and drink the milk and wait util help arrives.