There are plentiful medium-sized supermarkets throughout San Pedro [1]; the cheapest is Super Buy on Back Street. The best selection is at Island Supermarket (on Coconut Dr., tel. 501/226-2972), which is large and modern, and offers free delivery.
Wine de Vine (tel. 501/226-3430, www.winedevine.com [2]) has the finest selection of imported wines in all of Belize and a world-wide selection of cheeses and meats. They offer free wine tastings and also sell by the glass. The new location is on Coconut Drive before Island Supermarket.
Pinguino Wine Company (tel. 501/226-2930, www.pinguinobelize.com [3]) sells Napa Valley wine on its private Pinguino label, as well as gourmet olives and olive oil.
Premium Wines (tel. 501/226-3700) on Front Street has a selection from seven countries and offers wholesale pricing: Buy 12 bottles and get a 17 percent discount. Prices range from a US$12.50 California wine to US$130 for a French white table wine.
Links:
[1] http://www.moon.com/destinations/belize/the-northern-cayes/san-pedro-and-ambergris-caye
[2] http://www.winedevine.com
[3] http://www.pinguinobelize.com