if you haven't tried using tampons before.. i'd suggest you buy some and try before going for the trip..
it's not easy to insert it in.. and some people might find it painful and disturbing. you wouldn't want to be suffering instead of having fun during ur holiday.

most of my friends opted for the pills.. they'll delay ur menses. i don't think there is a need to worry about taking pills as an unhealthy choice.. it's not like you go to beach every month for holiday..

if you want to gamble ur way to a more natural way,

drink pineapple juices if you want ur menses to come faster;
take black pepper if you want to delay ur menses.

Snorkeling?

Beware of sharks. When I was snorkeling Langkawi, they're using blood soaked chicken parts to attract the sharks to the shore.