When I were a lad, whenever I went out into the bush to do a little impromptu shooting, my method of carrying ammo in the field was simple: the carriers were called “trouser pockets”, and I would just fill them up with loose rounds of ammo (whether .177 pellets or .22 cartridges).
But le temps se marche, if you’ll pardon my French, and now I need to carry my plinking ammo in some kind of carrier.
Of course, if I’m carrying a gun that shoots from a magazine, carrying spare ammo is not an issue: just MOAR magazines. And indeed that’s what I do, in that I have multiple spare magazines for all my semi-auto guns.

But what, I ask myself, do I do when I’m carrying a single-action revolver or a tube-fed rifle?

Sure, I could just keep the boolets in the box they came in, or jam ’em loose in my pocket as in times gone by.
But that means fumbling around, and getting them to line up to be reloaded and all that.
Then I read this article, and it made all sorts of sense to me:
A convenient solution I have found is the magazine for an M1911-style .22 Long Rifle pistol. The slim magazine can be conveniently carried in a pouch or pocket, with the rounds protected, and individual cartridges can be thumbed into a single-shot chamber, the magazine tube of a rifle or the loading gate of a single-action rimfire revolver.
I’m not sure about a 1911-style mag, because those tend to be spendy. But any old cheap .22 pistol mag will do, surely? Like this one:

That’s under $15 per mag, it holds 15 rounds, which means that four such mags would mean… [carry the 4] ten reloads for a Single Six revolver, or… [carry the three] five or so reloads for the Model 63. All in a handy little package, so to speak.

Definitely worth thinking about.