With all the strict weight restrictions in place with the airlines for checked luggage I wouldn't bring the soda from home. If you are going to bring it on the ship then just wait until you get to the port city and stop at a SuperWalmart to get your beer and soda.
The overweight luggage fee, about $20-30 for bags over 50lbs would be more then buying a soda each day.
I know Carnival offers free lemonade, iced tea, fruit punch, apple juice and orange juice all day. Is that an acceptable option for your hubby? We don't drink any of that at home but when on the cruise we drink the lemonade when we would drink soda at home because it is free.
I've also have a bottle of liqour leak on the way home. It was a carry-on in one of the cardboard liqour boxes they give you when you buy it. Well I smelled like Mango Rum for about half the flight home and can't drink the stuff anymore because of the smell.