Families observe St. Lucia's Day in their homes by having one of their daughters (traditionally the eldest) dress in white and serve coffee and baked goods, such as saffron bread (lussekatter) and ginger biscuits, to the other members of the family. These traditional foods are also given to visitors during the day.
Local (seasonal) fruits include: Mangoes, Guavas, Wax apples, Love apples, a few different types of “plums” passion fruit, sugar apple, soursop, starfruit (Karambola), tamarind, avocados and acerola (cherries (high in Vitamin C, locals call them barbadian cherries).
Virginia might be right about high end wine and liquor being expensive, but I have found that drinkable wine is actually a little cheaper in St.Lucia than in the US. Mid-level gin and vodka is roughly comparable to prices in the US (maybe a little more, but not enough to make it worthwhile to haul it in your luggage).