Did you read my post about transportation?
I am 51 years old, and was in the transportation industry for 20 years. I have also traveled to all 48 states, and Canada, and Mexico. Ten years ago I could tell you what almost every interstate exit in the lower 48 had for businesses around it. I have an Associates Degree, but most of my knowledge is self taught.
There is far, far more food shipped into the NE than is shipped out. Most grocery warehouses keep 3-4 days inventory on hand. How long would it take for those cities to burn once grocery store shelves were empty? DC would burn as well.
A smart military campaign could starve the big cities of the NE and Chicago in a couple of weeks. There are choke points that could be used to cut 80% of all ground transportation to the NE.
There are plenty of rural folks who, like us would be fine, but there is not enough food grown and raised in that region to feed those cities.
Are you not aware of the corn belt of Iowa, Illinois, Indiana, and Ohio? The dairy farms famous in Wisconsin, but all over the north? Fruit orchards in every state? Fishing along the east coast? The Great Lakes?
Just because food is shipped all over the country doesn't mean a particular region has to have it to survive.