Inventory is full

[001]

You need to drop/use some stuff so that you got space to pick up the pockets first. (Yeah, I know, bro...)
After that, you just buy medium or large pockets (medium are best, the large pockets are too expensive for what you get in space)

For the last part, it seems like you're talking about storage boxes. I really do not think anyone should be using those, as in the end, it's the same as dropping it on the floor.