Sand Lake Road is the heart of the commercial tourist strip so you will have lots of choices in walking distance for food. I forgot about the World of Orchids in Kissimmee! Worth a go.
Fresh open markets are few and far between, as I have not seen any since I moved but will check it out for you. As for Floridian cuisine you can not beat the Columbia, over 100 years old, terrific cuban style food, to die for...located in Celebration. You have email coming your way later, clock out time and din din.