some media to record on! I would say console. Its a large part of the chain. I can get use to monitors, I can get by with not so good mics, and most recording media sounds ok, you can't really go wrong with that!
If he's doing this for money? Tact. Or perhaps more accurately "conflict resolution skills"... And a good dose of hard-earned wisdom in knowing when to pass on a gig to start with.
I would say his hands, because they're good for turning knobs and plugging wires. After that, probably his arms because that's what his hands are attached to.
I'm pretty sure that the brain is recommended, but not a requirement.