every time someone asks this my answer is the same:
ZIPLOCS.
multi use in all sizes. to bring home wet bathing suits & sandy flip flops, store hot sauce & rum (ha, mine leaked and didn't mess up all my stuff), for seashells, keep your cash in them when toolng around (wallets, backpacks & pockets WILL get wet on a boat, and you will at one time or another be on a boat there), keep your shampoo/sunscreen in one, i've seen them leak all over a suitcase, i could go on and on....
drug store items are pricy there. i am a just-in-case girl, i bring advil, benedryl cream, neosporin, band-aids, immodium & pepto, etc. my ex thought i was nuts, but he was damn glad i had them, as he used them all.
have fun.