In my personal opinion one should never take cash as it too easily lost or stolen. Travelers cheques are the best choice. They can be replaced if lost or stolen. Credit cards are iffy. I chose to use travelers cheques on excursions and keep the charge card locked up in my stateroom safe. I hope this helps.
I suppose there is alot to be said for travelers cheques, but i have always just used cash on the islands. If your not comfy with that bring travelers cheques and cash 1, or whatever you need before you go ashore for the day. Sort of the best of both.