We flew into Union Island from St Lucia and did a catamaran sail with Captain Yannis. We picked up passengers at Palm Island, then went on to Mayreau, and Tobago Cays and back to Palm. It was beautiful. I would think that Palm Island resort offers a number of day sails to choose from.

We went to Palm Island Nov 2002 and absolutely loved it. We flew from US to Barbados and then to Union Island - 10 min ferry to Palm. We did not have a luggage problem but were warned about it as flight from Barbados-Union has to go on time as no lights on Union runway. We put stuff in carry-on to be on safe side.
We took 2 excursions both offered by resort on their boat. Snorkeling trip to Tobago Cays was good - beautiful water - stopped on little island for lunch. Only problem was water was rather rough at times so visibility not that great. On second excursion went to PSV - had tour, lunch in resort restaurant. Probably could have snorkeled there but did not. On way home we stopped at Mopion(?) alittle dot of an island in middle of ocean. Snorkeled there but didn't see tons - was rough at times also. But all in all we enjoyed both excursion alot and would do again. Tobego Cays is known for best spot to snorkle from P.I. It might be fun to go to some of the other islands nearby also but we did not do that this time.
You really don't need much $$ as everything is included and excursions can be charged to room paid w/credit card. We tipped some but didn't notice much of that going on - US$ is probably fine that is what we used for tips to excursion people and bartender,etc. We had to pay some departure tax at Union in cash (US$ fine) but I can remember how much it was. You may need $ if you would go back over to Union to shop/eat but again would think you could charge at most places.
PI is very relaxing - gorgeous beach, excellent food - can't beat the all-inclusive on drinks!!
We are planning to get back soon. Have a great time.