Breathing! Like, going and sitting somewhere and taking some deep breaths to clear my mind.
For me as well, being a Christian, it's the time where I say hi to God and ask for...well usually discipline and patience. And then I move on, knowing what I'm trying to achieve.
That covers emotionally and spiritually I guess.

Physically, being outside. It only needs to be wandering out in the yard with Riv, or going to the park. That really makes me feel alive.

Ideally, if I have time, I'll go walk and sit somewhere with my bible while Riv plays (throwing the good book aside and sprinting when I see him head for the road :P).
Most days it's walking out to the front step and taking a few deep breaths and stretching while saying 'hi God'. And letting Riv play in the front yard when we've just got home from somewhere.

Would love to hear other people's loooong centering time, and also how others grab some time to ground themselves when they're busy. Especially when you get to that point in your day where you feel like you're about to crack.