Mapping to End Hunger– New York City Coalition Against Hunger
This coalition has mapped food retailers, community gardens, farmers markets, food stamp offices, WIC offices, restaurants, and a number of other variables to understand access to food in New York City. The site does not have downloadable GIS data, but it does have a very good report about the project, plus a fascinating interactive map showing all the data in PDF format. You can also download the raw data on food sources in Excel format, which offers a good example of how to format data for geocoding in Excel.
An online map (and downloadable Excel file) of various food access and resources data aggregated to the county level. From the US Economic Research Service at the USDA.