Crafted bags that increase inventory size.
This would solve a few issues that I've noticed, mainly that the inventory size is very small come endgame and that leather tends to pile up. My suggestion is a crafted bag item, like a miner's bag or a forestry bag, that contain specific kinds of resources. They would take up the normal 1 inventory slot, and could be activated in order to access their capacity. Items of the appropriate type should be automatically sorted into the correct type of bag.