An elastic stock sleeve would rarely if ever spit out a cartridge. I find it funny hunting photos rarely show these yet many are carried in the field in AK. More than one hunter has slipped his off for photos. I don’t fill it all the way up, but keep 3 or 6 there. The cartridge carriers for the butt stock that have extra storage in addition to cartridge loops just seem to add too much bulk for a rifle that’s going to get shouldered quickly, probably with rain gear. There’s a permanent lipoma bump right above my bicep where the 375 didn’t get shouldered exactly right while practicing snap shots in good rainy conditions.
I’ve also taped three cartridges together with a single wrap of electrical tape with an inch long tail, for quiet carry in front pockets, and a few more in the pack. Without having to think I automatically know three are as easy to get as car keys, but it would seem fumbly if someone doesn’t use taped cartridges the rest of the year, and rain gear makes reaching front pockets a little work. Between six in front pockets, six in the pack and what’s in the stock carrier, that’s a full box of ammo.
I like the idea of a cartridge holder on the belt, but have never used one since it interferes with a pack belt, although placed on the pack belt can work if you have room. I don’t want anything on my wrists so I’d pass on wrist carriers, but they might work great.
One of the holders that keeps a couple on the stock near the receiver could work as long as it’s not right where the carry hand wraps around the stock. Some like one of the slings that hold a couple, but that extra weight swinging under the rifle never excited me.
Rain gear and your day pack belt will complicate most options. With the butt stock always in the right place and easily accessible it’s a natural.