It is customary to tip at the resorts and dive shops when you leave so place it in and envelope and drop it with the desk or in the box provided or even hand it to the one you want to give it to.
Do not forget the dive masters and boat captains if you have been diving.
Everyone here owns a gift shop and most are even worth taking a look around in.
You can find that special gift to make your friends envious back home. Remember to haggle with the sales person.