Located at the rear of the Catholic church, two blocks inland from the Cruz Bay [1] waterfront, Raintree Court is home to the best store for beachwear: Love City Surf Shack (340/693-735) has swimsuits, tank tops, surf shorts, and other surf gear (never mind that surfing opportunities are minimal on St. John).
Across the street from Raintree Court, in a cute yellow and pink building, is Pink Papaya (340/693-8535), a venerable St. John [2] gift shop with a nice selection of art, jewelry, and accessories.
Links:
[1] http://www.moon.com/destinations/virgin-islands/st-john/sights/cruz-bay
[2] http://www.moon.com/destinations/virgin-islands/st-john