Yes, they do sell wine in grocery stores here in Tampa. But, I'm not sure about you finding a grocery store en route. You are going through downtown areas, mostly industrial. There must be one somewhere, but it won't be easy to find and you could run up a higher cab bill. Look for alternatives, such as convenience stores, liquor stores, etc. Also, make sure Carnival will let you take all of that on board.
Liquor store is probably your best bet. Ask the cabbie to take you to one on the way,,,there are liquor stores on Kennedy Blvd, on the way, and another I can think of on North Dale Mabry Highway, pretty much on the way also. Don't let him take you very far out of the way, as both of these liquor stores are no more than a couple of blocks out of the way. Have a GREAT cruise.