Training on vacation?
You should be fine getting in some runs and swimming.
It is great working out on vacation - all new scenery, routes etc.
Also makes you feel less guilty when eating "vacation" food.
Enjoy...
RV
It takes a long time to get good. - Scott Molina
Slow is smooth; smooth is fast. - Rich Strauss
Mav - I have had this same issue and will also be in the Carribean soon on vacation. One thing I have done in the past is to try and time my workouts so that my vacation week lands on a recovery week - sometimes mmoving things a round to accomdoate this. Another option is to do a sport focus week - maybe swimming - swim every day for longer sessions and focus on your limiters. Since I will be in Grand Cayman doing some diving I plan on swimming as well but will focus on running speed work there as well since I will not have a bike . As far as losing fitness as long as you do something avery few days you will not lose a thing in just 6 days, in fact you would lose little if you did nothing in that short period of time - but you may fall a little flat and mentally not like doing that either - have fun sailing - I ahve sailed there before as well - you will love it.
If it's only 1 week, you'd be okay with not doing anything at all. You would probably come back and be the same as when you left. Running and swimming it the Virgin Islands never hurt anyone though...

With my 1/2IM said and done I'm taking this week off/very easy. Next week, though, I will be sailing in the British Virgin Islands for six days. I know I won't have access to a bike but I would like to do some sort of tri specific activity during this trip. I know the sailing itself will be somewhat physical but I don't want to lose any fitness with my summer season picking up a few weeks after my trip. I plan on swimming and trying to squeeze in a few beach runs along with some calistenics (sit ups, squats, push ups) but I was wondering what most people would do in my shoes. I don't really plan on doing anything in excess but I'd like to be somewhat active so I don't feel like a sloth.
"I run because it always takes me where I want to go" -Dean Karnazes