Though cap & ball revolvers lasted well into the cartridge era, folks who carried them would still have had to carry reloading supplies regardless if they used the extra cylinders for quick reloading as these would need reloaded eventually as well.
Many may have carried the paper cartidges and relied solely on those if they were within what they felt enough miles of a general store or trading post to resupply.
My guess is that most who carried a cap & ball revolver on the frontier also carried a cap & ball rifle so they would have these reloading supplies in their shooting pouch with their rifle reloading supplies; cap, ball, flask, grease (wagon wheel grease would be very common)...
Hickock carried two revolvers in case one misfired. Most shootist of that time carried two revolvers, but as we know, they had to reload also.
Hope this helps.