Basically we'd almost all starve to death. Transporting food would become uneconomical. Hell, harvesting food would become uneconomical. The trickle of food which got into urban areas would sell for insanely high prices. The rich would still be able to afford it for a while, but with the whole economy collapsing and widescale starvation the rich wouldn't stay that way for long. Rural folks might be able to survive for a while, until the looters came pouring out of the cities and into the countryside (on foot, presumably) looking for food.

Eventually we'd be able to re-establish some kind of civilization (pseudo-steampunk?) with a severely reduced population, but there'd be all sorts of bad stuff to happen in between now and then.