If you're willing to take a long walk, there's a CVS at 2400 Jefferson Davis Hwy as well as a Metro Commuter Store somewhere in the CC Underground (1615-B Crystal Square Arcade). The CVS is closer to the southern/Viaduct side of the airport whereas Crystal Square Arcade is more accessible from the northern end via the Mount Vernon Trail (which has an underpass between 15th and 18th St. S).