I have these little drawers I got on clearance in my extra (one fan controller, one optical drive, and then these drawers, which I'll use to hold the various small bits that can accumulate. I use a wireless mouse/keyboard (mostly) and I prefer rechargeable batteries, so I'll always keep a charged set in the drawers, plus if I have like headphone adapters or USB dongles that I'm not using at that particular moment. I'll also put spare case bits in there, like case screws or MB lifts (if that MB didn't need as many as were given with the case).