`I generally carry my horn on my dominant side (right), with the gun carried in my left hand. If the gun is on a sling, I carry it muzzle-down on the left shoulder so the hammer/cock is on the outside. This makes for a convenient method of taking it off the shoulder with my right hand in the correct place and the butt easily shouldered for a quick enough shot.
Of late I have been carrying two horns, one with my quickly depleting supply of 3f Old Eynsford and the other with 2f Triple Seven. With black powder in such short supply and all black powder substitutes having such poor reliability in side-hammer guns, I find it expedient to use 15 grains of the OE as a "booster" charge with fifty grains of the Triple Seven atop it as the main charge. This will, I hope, extend my supply of black powder and help get rid of the Triple Seven pending the arrival of Estes' black powder (hopefully) sooner rather than later in 2023.
I'm still experimenting with the height of the horns, but the general consensus here is to carry horns at about elbow height, which seems comfortable and workable.
My "main" possibles bag is October Country's Couer d' Alene model which allows for.... well.... everything I need for shooting/hunting/adventuring with room to spare for a light lunch, a few survival bars, an apple and maybe a small bottle of water. Shooting components are switched out depending upon what I am shooting, i.e.: flint wallet/capper, different caliber projectiles.
I used to carry the horn inside the bag, but this never really worked out very well. I also once carried everything inside a Jansport klnapsack. I missed a squirrel once though. He continued to sit on his perch scolding me while I got my pack off my back and reloaded the old T/C Cherokee .32. Brave squirrel. He made for a great stew, but I still switched to an old purse until I got a proper possibles bag.