You have a very nice outfit there!
Not a criticism, but just a couple of historical notes... The metal container with the magnifying lens is actually a tobacco box, and not a tinder box. Obviously, you can carry anything you like in it, but it was intended to hold tobacco, and the lens was there for lighting one's pipe, although you can certainly use it to start a fire. There was a nice article about these in a back issue of the Museum of the Fur Trade Quarterly (see "Iron Tobacco Boxes," by Charles Hanson, Jr., The Museum of the Fur Trade Quarterly, Vol. 9, No.1, Spring 1973). Dr. Hanson indicated tobacco boxes with the burning lens in the lid were being sold by the Hudson's Bay Company and the Northwest Company by the 1790's. I'm not sure how that will fit in your time frame or location. Evidently, similar elliptical iron tobacco boxes without the lens were being traded much earlier. I don't think Dr. Hanson commented on brass as a material for these. It was my impression that japanned sheet iron was most typical for the types with and without the burning glass. Ted Cash Mfg. does sell both types (with and without the glass) in a tin plated iron version, although he does call the plain one a "tinder box." I'm sure one of these would be great for carrying your char cloth, but if it were me, I would probably carry the flint and steel separately.
Carrying a flint and steel in the tobacco box seems logical, but the flint or the hardened steel may scratch the magnifier or knock the lid off the container as it jostles around in your pouch. At the very least, they will make "clinking" noises unless well padded, and will likely pulverize any charcloth carried in the tin with them.
One other thing is that I have actually been researching some of the archaic terminology, and the pouch you have there would have more likely been called a "shot pouch" in the time and place you have in mind. The term, possibles, in reference to one's personal belongings, is a 19th century western term, evidently borrowed from the Spanish posibles, meaning a person's goods, property, or means. Several of the chroniclers of the mountain men of the southern Rockies made reference to the "possible sack," which was a very large container made of buffalo hide, used to store a fellow's extra clothing and other odds and ends, like a razor, extra lead, skins for moccasins, souvenirs, and possibly some bedding. It was always a possible (singular) sack (not bag). The most common term I've found in the early 19th century literature for that over-the-shoulder container is "bullet pouch," although "shot pouch" was still sometimes used. As far as I know, the term "possibles bag" is a late 20th century "reenactorism."
Again, you have some nice kit! I hope you enjoy it.
Notchy Bob