Congratulations on the booking, davephillyj! I'm so excited for you! Carnival Fantasy was the first of 8 sister ships built by Carnival, making the Fantasy class among the most successful (if not the most successful) ship design for the line. I like Carnival -- not my first choice, but our last two cruises on the line were fantastic and I would not rule out the line for future cruises. True, there are fancier lines out there, yet sometimes you just want to kick back. Also, Carnival is one of few lines on which I enjoy the buffet lunches. IMO, the Mongolian Wok is not to be missed.
As for packing -- given the itinerary, at least two swimsuits, water shoes if you wish as well. T-shirts/shorts will be great for Nassau and Grand Turk and for your sea days, but be prepared for the A/C on the ship. For evenings, you no longer need tuxedos and gowns, although some pax still dress up. This page from Carnival's website
will help you decide on the clothing to pack.
If you haven't done so yet, be sure to purchase travel insurance, preferably a policy that includes coverage for trip interruption. You can compare policies at InsureMyTrip.com and, of course, ask any questions here. Just be sure to do it very soon as most policies will cover pre-existing conditions only if you purchase the insurance within a week or two of your initial cruise deposit. Even though you're driving to the port, you never know what might happen. One of my friends once broke her ankle getting into her car at home and had to cancel her trip. She had insurance, so was reimbursed fully.
Most importantly, have a great time and come back with a full report for those of us who are stuck on land!