I attach the powder horn to the pouch strap. And I have enough tools to keep the rifle running. I also carry a “ruck” when I leave the vehicle.
However, I hunt in some pretty rough terrain at times and unless I find it someplace in the back seat of my pickup I apparently lost a priming horn in a fall on a steep snowy slope about 10 days ago (too much stuff in the pouch pocket) and many years before that lost a prized knife that was attached to the back of the pouch to the same thing but no snow, slick tall grass on a slope, in the great white North.
I have hunted with MLs for number of years starting with small game in Iowa in the 60s (back when the DGW “Squirrel Rifle” was made in Belgium). I have spent time on foot and horse back in “occupied G-Bear habitat”. Which is basically the entire National Forest I hunt in. I fallen into creeks, had a “horse wreck” in a beaver pond. When I got out I had 2” of water in the pouch but kept my rifle dry somehow, powder in the horn was dry. Had I had it in the typical flask, for example, I doubt it would have been. So I do things differently than someone hunting pheasants in an Iowa cornfield might. I do what works for me. Everyone else should too.