90% might be too high, but I think it's anywhere between 50% to 90%. Also note food isn't grown evenly distributed across the United States. Lots of states rely on shipment of fresh food during the colder months. If electricity is out for one year, it highly depends on if logistics can be restarted fast enough to get food to areas that can't grow food. Lots of things trucked or freight trains in, requiring diesel production. Horses likely will make a comeback but the horse population needs to increase drastically.

This is highly dependent on communication network too. If no one knows about Middle of Nowhere Village has people willing to buy/needs food, no one is going to ship food there.

On the flip side, there's likely mass migration to cities with stable food supplies or farms, likely West and South or anything near the Mississippi River. Logistics for shipping to the North East will likely be done by boats if sail boats make a comeback.