Most folks in the US are carrying around lots of spare calories on their person everyday due to being overweight, even just 10 lbs over gives you 35,000 calories you can burn. And a lot of people, myself included, have access to a bit more than that.

So I'll put forth the idea that water is the most important part of this equation, not how many mre's or whatever else food wise you think you'll need for a journey of this type.

In a scenario where you'll need to walk 400 miles, obviously things have deteriorated way beyond any semblence of normal life. In my opinion people will have to adjust to the idea that surving this isn't going to be comfortable with 3 meals a day, but just surviving to live another day to continue walking is all that's to be expected.

And I have my personal opinions about the ability of people to walk 400 miles, or ride a bike for 80 mi/day....and for the general populous it's not favorable.