Hi Jen,
I get carsick easily, as does my DD(10), so I did lots of research before our first cruise (7-day Western on 2.24.07 - awesome!). I brought Bonine, Dramamine, Ginger, and seabands with me - I was prepared!
In the end, I personally took 2 24-hour Bonines every morning when I first got up, and they worked like a charm. I had done too much planning to leave it to chance, so I don't really know if I needed them or not, but I do know that with them, I had no troubles.
My DD used the seabands a few times - particularly during the sail away party and the first night (the Florida straights are wavier than the Caribbean) and then on the at sea days.
We experienced fairly calm seas throughout our cruise (usually 4-8 ft waves, with the worst being 14 feet or so nearer to the end of the week). So I don't know if it would have been worse if the seas had been rougher.
Anyways - if you are worried about - be prepared, and an oz of prevention is a good strategy!
Have a great trip!