Besides mini marts inside the resorts, you best bet is one of the grocery stores. If you want to shop prices for specific brands, the four stores are all within walking distance. The grocery stores are located about half way between the airport and Ocean Club.
DD, there's also a duty free shop just past the luggage carousel, but before you clear customs, in the airport if you want to make a liquor purchase there. It's especially convenient if you're waiting for checked bags anyway.