You can't get more organic than by growing the food yourself but unfortunately, most people who live in the city don't have that luxury. Instead, you are forced to pay a premium for quality food. There is, however, a concept called Agricultural Urbanism that may change all that in the future.
Basically, the idea of Agricultural Urbanism is community-based farming on a grand scale. Each urban district will have one of these mega-structures which allows citizens to grow their own crops as well as sell off the surplus to help with their incomes. The building itself will have many terraces dedicated to a variety of vegetables and be built to allow the maximum amount of sunlight to reach the plants.
Water Spanning Vertical Farms
Urban Awareness Gardens
The Agricultural Urbanism Concept May Just Eliminate the Supermarket
By: Alex Scott - Published: Mar 17, 2010 • References: yankodesign