Age, gender, sexual orientation, disorder, what you did with them during the contact (ie., therpay, testing, treatment planning, etc) and how long you did it for. You should log it each time you see them. I suggest using time2track.com. You have to get a subscription, but its not much. My program pays for ours. Its well worth it.
PS: You should also be tracking your non face-to-face hours, such as supervision, test scoring, progress notes and assessment report wrting, didactics, rounds, etc.