A couple of points to remember when travelling to the islands:
Take cash money with you as there are no auto telling machines from which to draw cash on the islands. Try also to have smaller denominations which makes change easier.
Take insect repellent – there are all types of bugs on the islands. It is also a good idea to take a topical antiseptic in case a bite turns septic. Don’t forget your sunscreen – you will experience lots of sun! Packing a small torch/flashlight (LED ones are the best) is always a good idea because you are sure to be walking along the beaches at night.
The ferry’s timings are often very inconsistent so be as flexible as possible when travelling by ferry. This is especially important when leaving the island. Don’t leave your ferry departure until the last minute as you could land up missing your connection on the mainland due to a delayed ferry. Rather get to the mainland with time in hand.
If you know when you will be returning to the mainland it is a very good idea to confirm your return seat on the ferry when you land at the pier or jetty. This minimises any problems with seats when you are pushed for time later.