If you have a bunch of small, used, jumbled-up fasteners, just chuck them in the bin. Small fasteners are cheap enough that it's not worth sorting them.
I have a storage bin rack on my garage wall, with one bin each for (new, used) * (nut, bolt) * (M4, M5, M6, M8, M10). (Actually, in practice, I don't have enough of anything except M6 to justify separating new and old, so only M6 is broken down that way).
But if you keep them sorted it saves a lot of time.