Yup, a notebook. I rotate among four locations (left/right, top/side), and I record the date, time, and location, and I make a note if anything untoward happened: if the shot hurt more than usual or I forgot to aspirate, bled a lot, or was sore after the previous shot.
I keep the supplies in a small Pelican case, and the notebook and a pen live there, too -- just part of the routine.