Deep South.....
Some areas in the Southern United States could be OK, away from the major cities, but without modern seeds/machines and meds, there would be real problems quick. Breakdown in Transportation, food stuffs wouldn't be the problems, growing food without seeds, most modern seed can't reproduce themselves to the same quality type plants over a period of time. Pest Control for some type plants. Cattle and horses wouldn't be a problem, except need larger cities. Storage wouldn't be a problem, most people still put up food in Jar's, also dried food is easlier than you think. Still all those people coming out of big Cities, Atlanta/Jackson/New Orleans/Moblie and Jacksonville would be bad. The more advanced/rich you were the harder life would be..Life along the coast would be almost impossible, lack of clean water, epidemics, flies/bug and the soil is very poor in most places.
Interesting topic....
Orion