I have this problem, I buy ammo in bulk, shoot a small percent, and buy again... always thinking I am out... whenever i see a sale, I load up...
I did an inventory a few years back, and I was at some 17K rounds of various (.22lr up through .308 and all inbetween, us .223 and rusky 7.62x39)....
And for some reason, I do the same with canned tuna/salmon/spam, and beef jerky.
I figure any zombies come my way I can hold out for quite some time...
I don't quite have the water resorces set... but living in las vegas now... I should think about it...