I try to keep about 250rds. each for all my hunting rifles; also 2,000rds. of .22RF.
I just picked up my new AR last Friday, and have 900rds. worth of LC brass, powder, CCI Arsenal Primers, and 55/62gr. bullets.
I don't reload for the shotguns, but keep about 200rds. each in 12, 16, and 20ga. around - slugs (16 and 12ga), large shot (all 3), and bird shot (all 3).
I keep a couple thousand primers on hand in L rifle and S rifle. I don't shoot handgun, but am about to get back into it. Have dies for .45ACP, .38/.357, .380, and will be buying for .40S&W.
Based on my available range time, I picked the quantities of rifle rounds so that I can completely rotate my loaded inventories every 2 years.