One major challenge (and i don't have a solution for) is footwear.
Almost all footwear is manufactured in ways that result in an unrepairable shoe which lasts only a season or two.
Consider that the average North American is on the verge of obesity (heavily overweight). They walk maybe 1,000 steps per day, and that's almost exclusively on flat, level surfaces. And most likely indoors for 90% of that.
Fashion footwear is completely impractical, and everyday footwear is engineered for that market I just described.
Which leaves us with outdoor and athletic footwear. Trekking boots are an option. But they are designed for occasional use on groomed trails. Army boots are engineered for long marches and are probably your best boot option. But you can run in boots without extensive physical conditioning, and even wearing boots day in day out often causes knee issues for the average Joe because of that extra weight.
Running shoes are designed to be thrown away after 6 months, and are not designed for lateral movements. That leaves trail running shoes and things like tennis shoes. All of which are not designed to last more than a year.
The other issue is you. I grew up in bare feet, and kicking around rocky shore lines. Moving to North America, I was shocked at how weak the average person's feet and ankles are. I'd bet that most people couldn't run the length of a football field in bare feet without injury. It's not just a lack of lower body development and excess weight either, it's also a lack of coordination and the brain's unfamiliarity with navigating uneven surfaces.
I am telling you right now that post solar kill shot, every surface is going to be uneven! Debris is going to be everywhere.
You Need to prepare your body and mind just as much as everything else.
As far as footwear goes, I would go for a pair of quality army boots, and a pair of trail runners. Preferably, the boot uppers are glued and stitched to the soles, but they are very hard to come by (army boots aren't made that way anymore).
Footwear will be available immediately after the collapse, but they will be mostly impractical, and the ones that are actually useful, will fall apart in a matter of months of daily use in ways they were never designed and made for.
You may have to be making your own footwear sooner than you think.