Thanks for the replies guys!
I got my introduction to ML shotgunning back as a kid, back when Starr was still active in SoDak. I hitch-hiked up there to see him a couple times. As I recall he was a promoter of carrying supplies in hunting coat pockets, but I've never been a fan of hunting coats. Tried carrying stuff in the pockets of my field jacket but never got comfortable with it.
My usual setup is a double-pocket hunting bag with powder horn on a separate strap. This works well for rifles and muskets, but the rifle bag didn't want to carry all the "stuff" I stuffed in it. (I suspect the bag secretly resented carrying a capper, caps, and nipple wrench.)
I'll probably go with a similar rig for the shotgun. My default bag pattern (copied from an early double-pocket bag) should work out well. I'd not considered building a shot flask into the bag body--I was thinking about a shot snake on the strap. I'll have to play with that idea some. How much shot are you carrying in the integral shot flasks? I like the idea, carrying the shot flask in the bag just felt awkward.
Amount of shot to carry is a bit problematic. Since steel shot came in, duck hunting with an ML is almost more bother than it is worth. Doves are still an option though--and I can miss a lot of doves! I've seen days back home when I'd get 50+ shots at doves in an evening (pass-shooting waterholes). Sometimes I'd even manage to limit out before dark.
The rest of the time though, 10-15 shots was about it. Maybe make a flask integral with the bag to carry a pound of shot, and add a shot snake for dove hunting?
Wads are not a problem: I've stuck with Starr's system of using 3 card wads, two over the powder and one over the shot. Works out well. With a double bag I can just carry wads in the front pocket. I can carry tools and spare caps in the back pocket, along with a few round ball and maybe some buckshot.
So, double bag with wads, caps, and tools in one pocket, wads in the other. Integral shot flask holding a pound or so of shot, add a shot snake to the strap when dove hunting. Powder horn and measure on a separate strap.
Capper somewhere--any recommendations for a good shotgun capper? After wrecking the inline capper I was using, I'm thinking maybe one of Ted Cash's Rifle Cappers would be a good choice.