I buy in quantity when the prices are good. That generally precludes me from buying ammo when the supply is low because prices are usually bad in that situation but there have been some unusual circumstances where I needed a box of an odd caliber (not one I keep a good stock of) during a panic.
For those situations, my rule is that I will not take any more than I need and even if I can't get all I need, I won't clean the shelf. I will not take the last box of a given caliber off the shelf. That's what freaks people out--seeing that there is absolutely no more X on the shelf. Even if they weren't concerned before, now they will be. Sort of like the stupid TP thing we just went through. It wasn't that there was really a shortage, it's just that a few knuckleheads went and cleaned off the shelves, and now even the reasonable people start wondering just when they're going to be able to restock on TP when they run out. So they go to the next store and if there's some there, they maybe buy a little more than they need because of the induced uncertainty--if there's none there, then they go to the next store and buy all they can because now it seems very urgent.
It doesn't take much to freak people out. I don't want to be part of the problem.