The Russian double pouches for the 91/30's work great too. I have a bunch of them, each one set up for specific rifles, or Bessie. For rifle or musket I keep powder cartridges on one side, then cleaning supplies, extra patches, (I load my patch and ball from a loading block) extra flints or caps, some spare balls, etc. Sometimes I will dedicate one side/pouch to the pistol, and the other to the rifle or musket, and then keep anything extra in the pack. But I prefer to have all the "stuff" on my belt, so I can do any maintenance to the rifle or pistol without taking off and digging into the pack.
For my cap-n-ball revolvers I just wear a capper around my neck, and then a small pouch that holds non-combustible paper-bag paper cartridges. Each contains the powder, wad, and a ball. tear open, pour in powder, seat ball and wad, (or wad and ball) and cap. Shazam! I carry those cartridges in a small leather pouch, only about a dozen or so, and a tin of caps.
As I am totally OCD on weight, (less weight, more food and water, and longer endurance) I've always considered spare cylinders too heavy an option. A lot of weight for six extra rounds.