Publix also sells wine, and is right in town. If you're driving yourself, it's an easy "detour" before you get to the port. If you're taking a Disney transfer from the airport, you'll have to grab a cab.
This one is just south of the port on A1A:
5645 N Atlantic Ave
Cocoa Beach, FL
(321) 783-1014
This one is right off of 528 (the Beach Line), which is convenient if you're driving from the airport or from WDW:
1850 N Courtenay Pkwy
Merritt Island, FL
(321) 986-6260
If you're driving yourself with a rental car, then I would definitely NOT purchase your alcohol at the airport. It'll be cheaper if you stop on the way. However, if you will need to get a cab from the port, that expense might make it worthwhile to simply pay a little more at the airport. (I'm sorry that I can't offer more specific advice, but I don't buy the alcohol in my family, so I don't really know what the difference in price will be between Publix and MCO.)