Hi, Ashley!
Congratulations on your upcoming Disney cruise to the Bahamas! Generally speaking, Bahamian weather is usually sunny and warm but can be a bit more unpredictable in the fall than any other time of the year. You'll probably experience temperatures somewhere between low 70s-mid 80s F, and the islands can get fairly windy with an ever-present possibility of afternoon showers. So, just stay tuned to your favorite weather forecast provider either online or on your phone in order to know before you go!
There is so much to do and see at
Castaway Cay that you can make it as active or passive as you'd prefer. Some guests like to plan Port Adventures for Nassau and take it easy at Castaway Cay, and then some guests prefer to wander the streets shopping in Nassau and hit the ground running with a full day of excursions on Disney's private island. Your itinerary is up to you, and your idea of "vacation." Without knowing the ages and preferences of your group, I always suggest a
Nassau Port Adventure which includes the Atlantis Resort -- my favorite is the water park, the Aquaventure.
As far as planning, make sure you make any bookings for onboard activities such as adult dining, spa experiences and nursery reservations (for those under 3). And you really won't need a lot of cash on your cruise. You may want to bring around $100-200 in currency to tip your room service crew, to take a cab in Nassau or to shop at the straw market there. Otherwise, your shipboard account is all you'll need on board and at Castaway Cay. I hope this helps you plan. Let me know if I can be of further service to you.
Have a wonderful day and a magical vacation. Bon voyage!
Andi