Hi, Tajmia!
Your 8-night Bahamian cruise from New York City aboard the Disney Magic is going to be divine! That's so cool that you get a one-day Walt Disney World Park Hopper ticket with your cruise fare!
You can bring bottled water on board the ship -- just pack it in a bag to be checked in once you arrive at the terminal. In addition, you can avoid the hassle of hauling your water by having bottled water delivered to your stateroom. Check out the
Gifts & Amenities Page on the Disney Cruise Planning Center on information about how to order 6- or 24-packs of bottled water.
With all the food which will be available to you (even 24-hour room service), I'm not so sure that I would waste space on packing snacks. However, you can bring pre-packaged, unopened snacks on board, too. You just can't bring personal coolers or perishable food items. I hope that helps you plan.
Have a wonderful day and a magical vacation. Bon voyage!
Andi