This may be a stupid question, but we are first-timers, so we're trying to think of all possible questions BEFORE we go. What do you do with your passport and other things when you go on an excursion that requires getting wet-ie-snorkeling or diving? Is there a place to lock up your personal belongings etc...or do you need to put things in waterproof bags and take with? Sorry if this is stupid, but we'd really like to know. Thanks!