What you do is...
You take the paperclip, insert it into the banana, insert the banana in the donkey, and BOOM! The donkey is buoyant, you've got yourself an easy floaty to the other island.
You could also...
Use the paper clip to defuse the bomb the evil Ian Compton put on the island, kill the donkey, eat the donkey, and use the banana as a helicopter to fly on over the the other island.