Most things today are shipped JIT Just In Time.
Walmart doesn’t have tons of stuff “in back”. Most stores these days don’t have a back. They have only enough to stock what was sold since the last truck.
So as others have said; stock what? Everything? And where would we keep it? Yes like the strategic oil reserves; we could have baby formula; hamburger, diapers, and powdered milk… but it is way easier to slap idiots who price gouge.
I volunteer to hold the strategic baby back rib reserve….