I have an entire binder. I'm a vet tech by trade, so everything is a medical record to me.
I have a section that I record his temp/humidity readings on about every other week (used to record every day-now I just check daily).
I also keep track of date of food offered, its weight, gender, and if he ate it our not.
I weigh him post every shed / poo that he had and record that
and finally a "notes" section for when I notice things like a discolored scale or strange behavior, cage cleaning dates, and other husbandry related topics.