That looks like a nice bag Jon. And if I were into period wear I would probably use one similar. In fact I do have one that I have hanging on my ML gun rack along with a couple powder horns. My bag is equipped with an antler horn powder measure and a home made patch knife with antler handle.
But I prefer my multi-pocketed cordura bag that carries all the tools I could possibly need to work on my caplock or flinter. Including spare ventliners and nipples and flints. It also carries my flashlights, drag strap, compass, TP, a couple first aid items, some speed loaders, extra cappers and of course plenty of room for those necessary snacks.
Oh yeah - and it comes in an attractive realtree camo pattern!