There is a selection of Coca-Cola products that are available from soda fountains, (Coke, Diet Coke, Sprite, etc.). Fountain drinks are available for no additional cost when you order them during meals at table service restaurants (but not when you order them from bars, snack bars, etc.). They sell a mug for $15 for the 3-night cruise, $20 for the 4-night cruise, and $35 for the 7-night cruise. This entitles you to unlimited refills of the fountain flavors. There are some additional flavors (e.g. Caffeine-free Diet Coke) which are available only in cans. Beverages that are only available in cans are always extra-fee, both in the dining rooms and elsewhere.
Unlike most other cruise lines, Disney will allow you to bring your own liquor onboard. However, keep in mind that you may not bring opened containers back into the United States at the conclusion of your cruise. Also, you must carry them onboard yourself... you may not pack them in your luggage.
You may also bring sodas if you don't think you'll be content with the beverage offerings available onboard. However, you must carry these onboard yourself as well. You may not pack them in your luggage.