I carry a bag and horn when I hunt, BUT...
I carry a block with two patched balls in it and two RMC tubes with premeasured charges in my bag. If I don't need to reload in a hurry, I'll do so from the bag, where I have a shot pouch with balls and a baggie with greased patches. I have an antler measure I use with the horn, and I can reload just fine.
I have those two premeasured charges and balls in the loading block in case I knock one down and it's not finished, I miss and they stand there (it's sure happened a few times!), or whatever might necessitate a faster reload.
I have not gone to traditional dress, and I don't ever see myself doing it. I like to be warm, dry, and comfortable as much, or more, than the next guy, lol, and while I'm sure there are ways to accomplish that in traditional dress, I have hunting clothing already, lol.
As for priming, I bought a little priming horn from a vendor at Lewisburg. I see him there every year, and at Dixon's every year. I should know his name, but I don't. I got my loading block and powder measure from him, too.
Anyway, I used to use a brass plunger with a valve. For YEARS. I like the horn better. A lot better. I find it's a lot easier to prime rather than pressing on that plunger valve. I just pour and done.