Your first liveaboard... wow!
Some things to remember:
1) Space is at a premium. Pack light: t shirts, shorts, bathing suit, stuff like that. You may need a very light jacket for evening after a day of diving because you can feel a bit chilled after all that time in the water. Luggage should be a soft sided duffle or similar bag that can be easily stored. Don't forget sunscreen, a hat, and sunglasses, any medications you need, etc. Also, you will probably need a paperback or similar reading material for your "downtime".
2) If memory serves, the vessel is based in FL. If so, it WILL be crossing the Gulfstream. This is a trip that will probably take the better part of a day either way. It is not always a smooth crossing, so make sure you take along a good seasickness remedy.
3) If you have specific dive gear needs make sure they are going to be met. For example, if you usually dive with DIN tanks you will need an adaptor for regular tanks. You might want to consider putting together a small "save a dive kit" in a large zip-lock baggie with stuff like o-rings, extra mask & fin straps, etc. Make sure it will fit in your dive duffle. Take only ONE wetsuit. At this time of the year I suspect you will need a full 1/8". But that is according to what *I* would need. You need to find out for yourself what you will need in the water at this time of the year.
4) Remeber that you are onboard a boat. This is a marine environment that will require some adaptation on your part. For example, water is at a premium and there are special type of bathroom aboard a boat that doesn't operate the same as they do on land. (BTW, the bathroom is referred to as "the head".)
5) What are your concerns about security? You will need to take your passport if you are going to the Bahamas.
You may find it useful to draw up a good checklist & follow it when packing. It will especially be helpful when REPACKING on your way home.
This is just the abreviated version. Hope it helps!
~SubMariner~