Well first, I believe, it depends alot on what specific caliber and type of ammunition you will be reloading, a few types of ammunition use the same type of powder. But, for example you wouldnt use the powder for a 12Ga shotshell in a .223 rifle cartridge. Also, you should NEVER substitute smokeless powder for black powder, or vis-versa. In addition you should NEVER mix 2 different types of powder or brands. Now, one eight pound keg(container) can reload thousands of rounds depending on the size/type if you're reloading handgun cartridges, and several hundred rifle rounds. So you should, probably, define your own requirements, and stock enough powder, and bullets, to reload atleast half of the reloadable cartridges in your arsenal. I myself keep three eight pound kegs of each type of rifle/shotgun round I use, and two for each handgun round I use. As far as trade and other uses are applied, I'd suggest buying a boatload of film canisters, and other slightly larger containers, seperate an eight pound keg of a few common type cartridge powders (for example Hodgdon is what I use, so their BL-C(2) for the 7.62mm, H335 for .223 rds, HS-6 for 9mm, 38 Super, 40 S&W and 10mm Auto, and it also works well in shotguns for medium loads) into several small batches and carry a film canister's worth... If you find a trade partner you can always come back with more at a pre-determined place. I would never recomend carrying a significant amount if you become nomadic, as you will essestially be carrying a large firebomb if you were to get shot. So in my opinion stocking up on more than a small amount should only be done if you have a safehouse or base of operations you can defend and keep others out of. And if you reload, enough to reload half your arsenal.