It's been different things at different stages of my evolution. One thing I noticed was missing a few months ago, was music.

I've been listening to music (anything, random stuff) at least 30 minutes a day. But judging by your recent notes, I'd guess you got that covered already. But keep this note in mind. At some point in your life you might start taking conference calls or listening to books instead of some music. Keep the music in your life's soundtrack.