My "stocks" depend largely on how many rounds of each caliber I tend to shoot. Handguns and semi-auto rifles tend to go through ammo quickly, so I keep more of that on hand than I do for some of my old bolt action rifles that I rarely shoot (or only shoot a few rounds through at any given time).
My most significant stock is in .22LR. Although I never really tried to stack this stuff high and deep, it's available cheaply and in bulk (under normal market conditions). As such, I had about 2,000 rounds of it on hand around Thanksgiving last year. Then, just as the panic was taking off, I had a friend give me a partial case of unwanted .22lr ammo that had been damaged in a shipment to his employer (who wanted the ammo disposed of). As such, I picked up quite a good bit of .22LR ammo at that time, with a few squished boxes out of the lot. So, I'd estimate that I was sitting on 7,000 rounds of .22lr right before the panic really set in. I was going to start giving it away when I first got it, then it suddenly disappeared from shelves EVERYWHERE. As such, I became more reluctant to part with it, and have instead slowly given some out to some close friends who I've found in need.