There's "keep" and "have on hand". The answer to the latter is "quite a few". I don't "keep" them until they've proven their worth. The "on-hand" powders were purchased in 1# quantities and are used for load development. They aren't "keepers" until I find a load using them that works well at which point I buy them in quantity.
As it stands right now, my "keepers" are Varget, IMR8208XBR, TAC, AA1680 and H4831SC on the rifle side and Unique, Clays and Power Pistol on the handgun side.
On hand, in addition to those above I have H414, BL-C-(2), Benchmark, Reloader 10X, Reloader 19, H4350, IMR4895, IMR3031, IMR4007SSC, Hunter, AA2520, AA2230, H322, H335, Supreme 780, Universal, AA#2, AA#7, H110, 2400, Herco, Bullseye, Universal, Trailboss and N340.