Howdy!
A good question!
First I want to say I carry a small shooting pouch, maybe 9" wide or so, and 9" deep. It has one small internal side pouch.(this is without measuring it, and I dont have it with me) I will discuss the contents of my pouch first.
I carry only what is needed to hunt or shoot inside my pouch, save for a small flint and steel kit which is in addition to my regular fire kit I carry in my haversack. The kit is carried in a tin made by hot dip tin, with a few other things, inside a brain tanned leather pouch.
Why the fire kit? I do not take my pouch and horn off in the woods, and sleep with them on. I do take my pack off which separates me from my fire kit. So the small one is for emergency cases if I were to be attacked at night by ye savages, or during the day when I had removed my pack for some reason. At least then I would have everything I needed to start a fire, and shoot on me at all times.
Back to contents; My precut and greased patches are carried in another tin, but a different shape from the fire kit. This way I can easily tell which it is by feel.
I carry a ball bag with about 12-15 balls in it. (A larger ball bag holding 60 balls is stored in my pack)
I carry in the side flap extra flints and a compass.
My powder measure is held with a piece of leather thong which is attached to the outter strap of my shooting pouch. I also have a vent pick and brush on a chain, but do not use the brush and prefer the bottom of my hunting shirt.
Two more things, a wing bone turkey call, and a period folding knife.
Now that you know whats inside, I will discuss placement. These above things are in their aproximate places always, and I know where they are by feel. The wing bone turkey call is always places upright along with the powder measure on the thong in the front side of my pouch. Then the fire kit pouch is next to that, again begin tubular and standing up. Next to that and towards the back of the pouch now is an oval tin (made by hot dip tin again) which contains my patches. After that and in the rear corner of the pouch is my ball bag, and folder, both upright.
It is packed and stacked good, and theres little room for anything else. When I go to reload, in as fluent of motions as I can I remove the measure, pour powder and dump down the barrel. The measure gets put back during my hands next trip into the pouch, saving a motion. After the measure is replaced, I grab the patch tin, remove a patch, and place it back in the pouch. Again not wasting a motion, I grab the ball bag while im in there, and remove a ball to place on the patch. The ball bag gets put back. I use a period practice of a looser ball and thicker patching, plus have eliminated the use of the short starter because it is not a historical item for my time period. All thats left is to ram it home, prime from the same horn, and fire.
As mentioned, it takes practice with doing this. I "ghost load" at home, meaning going through the motions without actually loading a ball, so I can learn and be more fluent with the motions and process. I only load from my pouch and horn anywhere I am, including hunting in kit. Even when I am firing just to shoot, I load from my pouch and horn. It works for me, and is what I love doing.
By the way, my horn is on a separate strap than the pouch. I put on the pouch first, then the horn over it adjusted so it rides just above the top seam and fold of the pouch. Both ride high on my right side, and are tucked under my arm.
And just to add, I carry a period ball puller and tow worm inside the wooden patch box of my gunne, in case you were wondering.
Hope this helps!
Simeon