A few months back, I bought a sleeping pillow (The Khaki Collection by Calvin Klein Home) which came in a nice, big zippered bag that I just couldn't throw away. It hung around my room, moved around some, eventually got a bit dusty, but I knew I could upcycle it for something. I finally found a use: yarn storage!
Since it's zippered, those wayward yarn strings can't escape. Because it's flat, I can't stack the yarn. That's a big bonus because stacking can sometimes lead to more disorganization--having to always shift yarns or getting lazy about having to rearrange everything once I've dug one ball out. Also, the flatness is perfect for discreet sliding under the bed. I've managed to comfortably store about 2/3 of my stash into this one bag and freed up four of my cute, reusable shopping bags.