Good news, you can bring a bottle of wine or champagne and some bottle waters or sodas if you would like! See the specifics below, taken from Carnivals webite!
A liquor and beverage consumption policy was created in order for Carnival to be able to control the liquor consumption of minors and the quantities consumed that lead to the disruptive behavior of others on board.
Liquor and Beverage Policy
Bringing Alcohol On Board - Embarkation Day:
Guests are prohibited from bringing alcoholic beverages on board. However, at the beginning of the cruise during embarkation day, guests (21 years of age and older) may bring on board one bottle (750ml) of wine or champagne, per person, only in their carry-on luggage. A $10 corkage fee per bottle will be charged should you wish to consume this wine in the main dining room; $14 corkage fee per bottle in the steakhouse. (A corkage fee is a charge exacted at a restaurant for every bottle of liquor served that was not bought on the premises)
On embarkation day, guests may bring a small quantity (package of 12 per person) of non-alcoholic beverages onboard, only in their carry-on luggage.
All alcohol/hard liquor/beer (sealed, unopened bottles/cans), wine/champagne over the allowable 1-bottle per guest (sealed, unopened bottles) or excessive quantities of non-alcoholic beverages (over 12 per person, sealed, unopened bottles/cans) will be confiscated and stored for safekeeping until the end of the voyage. The retained item(s) will be delivered to the guest̢۪s stateroom on the last night of the cruise. Unsealed liquids that are prohibited will be discarded, as well as any unclaimed items left after the voyage, and no compensation will be given in either case.