NYC has about a 10-day food supply in the grocery stores. A 48 hour disruption in food delivery could cause a big problem there and spark hoarding and panic. In most places it's the same story.
Our strategic grain reserves have hit an all-time low, partly due to the drought, partly to selling it/giving it away for food relief, and partly because we're throwing it into our gas tanks. With another bad growing season almost behind us, this fall looks to continue the trend.