When I was active in SAR (some years ago), my backpack was critical gear. I used ones that carried well and that did not shift when climbing, rappeling, or otherwise contorting my body. It had to hold an appropriate amount of gear (40 pounds plus), and stand up to abuse - thrashing through brush and rubbing against rocks. On various occasions, I would run with my pack. If it was good enough for those SAR applications , it was just fine for a normal recreation walk in the woods.

I have tucked one of those packs away beneath my bed, lightly packed with necessities. It would still work very well in a SHTF situation.