To teach people that food can be fresh, and it doesn't need to come from other countries shipped across oceans. Sanitation becomes less of an issue when dead things are not waiting around for days or weeks or months before they're eaten. There is such a huge difference between an apple that was picked a month ago and ripened in a box, and an apple you pick and eat right away. While a coastal existance might lead one to conclude this, America is still a largely aggricultural nation. Additionally, we export food world-wide.
Some food is imported, but many food stuffs come from the states.
Encouraging local growing makes a good story, but not economic sense. The reason for our giant aggribusiness shipping industry is because of division of labor. Certain foods are more efficient to produce in some areas. It is without a doubt a good idea to get real foods into kitchens instead of fast food for Amercia's youth, but there is a financing problem. You would have to raise the prices to compensate, which may or may not remove the people that pay full price.