I've carried a steno pad for the last 18 years of instructing. That steno serves as my record keeping for the FAA requirement (when they get full I file them - yeah, although it says three years, I have retained them since 1991 (maybe sentimental, who knows)). In addition to just the time I record my notes on that student ("high on approach, slow on final, etc.). I also record weather conditions and other pertinent variables (VOR check anyone? Is the flight school doing it, maybe or maybe not).

Your logbook will tell you the who, what, when. I want the bigger picture. After a week worth of instructing I would transfer to my official logbook. I keep the current logbook in a fire safe in the house. The rest are in a safe deposit box at the bank.