It would be so much better if this crappy old-school inventory system was scrapped. I have one round each of 6 ammo types - takes up all slots in my cargo pants... I have 30 rounds of one type - it takes one slot... Uh....
The solution is so easy and obvious: Just give all items weight, volume, max/minlengh, max/minwidth etc... and add those attributes to the containers. That would make it more realistic, and at the same time solve all "bagception"-problems.