A easy exploit for bagspace in this game is to use a hunting bag and stack different coloured mountain backpacks, each giving you an extra 10 slots a stack.
The more overpowered version is doing the same thing but with a Improvised Leather Backpack which is the smallest profile backpack (besides the smersh) in the game.
I was running around with 100 slots at one point... you are basically a human tent.
Not sure if this is working as intended but at the moment it feels like a cheat.
Cheers.