Yep. In an emergency the stores are basically looted by the panicked hoarders. Imagine if it were a BIG emergency like a nuclear exchange or pandemic!

There is an interesting article here about maybe the one source of supplies that the panicked masses cannot readily loot. I think he has a point since there has to be a HUGE amount of resources here:
http://www.survivaltopics.com/survival-blog/scavenging-dumps-for-survival/