In the last twenty years I made about fifty sketchbook journals, and these helped enormously whenever I was stuck on an illustration. I could look to the diary stock of sketches and the doodles of all the friends that I would ask to add something.
It's good to look back at drawings rather than a written diary, there is so much more information!
In 2001 I was a cleaner, and at tea time I developed the habit of quickly drawing the groups of people around me, this came in very handy as a supply teacher. I would enter the class with pen to paper, which worked a treat getting the class quiet, then inevitably I had lots of requests for portraits.