I bought a 10U rack to hold my AxeFX III and Helix Rack (yes, I'm spoiled and spend far too much on gear). When I was building this, I decided I wanted a drawer to hold all my spare cables, strings, picks, tools, etc.
It's hard to get excited about a drawer, but the quality of this unit really is excellent. It glides smoothly on its rails, the latch holds the drawer shut when you want it shut, but opens easily.
2U is enough to easily hold several cables, half a dozen packs of spare strings, some tools, bags of picks, batteries, zip ties and there's still room for a couple of mics or spare socks.
If you have 2U available in your rack, put one of these in it.