If I have to grab it in the middle of the night, stuffs coming down and I got to boog, My 16" CAR15 and my 870, and my Glock 17, + whats in my pants at all times, a 5 shot S&W 9mm with 2 reloads, + the 649 body guard with 1 reload, because that is whats available at arms length, in my bedroom. The Car15 has a 2, 30 round mags attached, and an aimpoint comp m3, the 870 has a 7 rd tube and a 6 shot side saddle, shot and slugs, the glock has a 28 round magazine inserted and ready to go. Well the body guard has 5 + 1 speed loader, that is for my wife when I'm not home. I assume we are bugging out in the truck, Glock 21 with 2 mags in there. There is a 50 round bandoleer of 12 guage to go with the 870, mixed shot and slugs.
Now if I get 30 minutes or more to get ready, all of the above + the M1a, and loaded mags, takes 2 people to load the ammo box. + the spare mags and ammo for the Glock 21, I have used the .45 acp more than most for hunting, mostly with 185 semi wadcutters, quiet and excellent for rabbits and squirrels, I have harvested 2 deer with 230 grn slugs, again, quiet at a distance. Not to mention food and water, bug out bag etc...
A method I have used in a jungle walk with lots of targets, and unknown obstacles, was a bird bag for hunting, 3 bags, which originally were 2 for shotgun shells, and 1 big bag for birds, and it is rubberlined to prevent blood from bleeding through, the big bag can hold 500 .357 easy, probably 200 .308 and 400 .223. For a lever action it would work perfectly. Rifle or pistol cartridges. I would say in .44, with all 3 bags, you could carry 500 rounds at your fingertip for loading.
I think the question is too broad, but as we go through it, maybe some cool stuff will come out.