If I were trapped on a desert island three things I would bring is....

1: Three things I would bring, Hmmmm, First I think I would bring a machete or some sort of knife. because it could come in hand if you have to slash some bushes, grab some branches or maybe even kill some wild animal's for food! (But be careful, it could be endangered!) and it can also be good for when you are first there if you need to get some seaweed off you, or even get coconuts from tree's!

2: I would also bring some water, because the island could have berries or other food, but then there probably isn't any fresh water! so it would be good to have some fresh water! but when the water runs out it could be a good idea to grab some coconuts, (with the machete!) and drink the milk that is held in it. and, believe it or not, the coconut skin is actually very good for your immune system and it will help you survive!

3: And also I would bring, A game! I mean, you never know when you'll get board on a desert island! and also its some good entertainment! ( me personally i'd bring my tablet/portable charger! )