I try to walk 2-3 miles a day. Since I am an old man, I figure that gives me a walking range of 12-15 miles a day if I have to walk out of somewhere. Since I keep to a sedate 4 mph at walking, I would be able to catch my breath quite a bit.
I spent four years in the Army as an infantryman in a light infantry brigade. We did quite a bit of walking. If you are in top shape, and you go for quite a bit, you can usually do 40 of so miles in a day. Of course there are tale of heroic marches where small units went 100 miles in two days, but they are just that, heroic. Being such, they are well out of the range of possibilities of middle aged middle managers such as yours truly.
So I am deeply amused by the macho survival crowd. The lean runners who feel that by maintaining their 7% body fat they will be able to play soldier in a first person shooter and win.
You see, my feeling is that if most folks are going to survive, they will not emulate the coyote as these folks are doing, but rather, they will emulate the porcupine. So I will waddle along slowly, keep my fat on (after all, gotta make it to the next harvest), and bristle with nasty spines (eg weapons) to make an unattractive target. It is not a bad ecological niche.