I tend to disagree with the 'near food' argument.

I want to be near people who provide valuable services; we're still going to have a functioning economy, just not based around the USD. A higher density population means I have more trading opportunities available within x radius than in rural, crop-growing areas.

Presumably, we'd outsource the import of food just as we do now: people would be paid to make it their job to transport enough food for the urban population(s) they service.

Also, social controls are going to be more important as government falls apart. No one hears a home invasion in the middle of no where. And fuel will be too valuable to constantly travel long distances just to make normal exchanges.

(I realized my post is kinda talking post-apocalyptic US, assuming the world is on par with the States' condition. Naturally if the USD alone plummets, the answer is 'outside the US.')