At the moment, my stash of yarn lives in a big, floppy, fabric bag in the mess that is the understairs cubbyhole.
So I bought a SMALL plastic box last night. Come lunch time, or this evening, I shall move much of the stash into it, and if I am REALLY good, will put a lot of the yarn into separate bags... so it won't tangle. Though... if it's in the box, that's probably not necessary.
I bought a SMALL box because I want to look at it and think, "Ohhh, can't put more in that!" not, "Gee, I've got room!".