If you have some singles already spun, and they are still attached to the unspun roving, and you want to put it aside (say there's a fire alarm or something, so you _have_ to stop spindling!) -- what do you do to store the singles and fiber and not have the yarn untwist?
If you want to stop spindling, what you do might be a function of how much roving is attached to the end of the single. If it isn't much (or if you are willing to break off the roving), you can just wind the yarn around the spindle up to and including wrapping the roving around. I usually wrap the unspun part below the cop, though I think that's just a personal preference. If there's a big ball of roving and you don't want to break it off, you could wrap the single around the hook a few times near the end of the spun part, and then tuck the spindle into the big ball of roving. If your spindle is hookless, or you want to make really sure the yarn isn't going to go anywhere, you could use a half-hitch instead.