I like to mess around with productivity systems and one of the most "fun" practices that I have come across is the Hobonichi Techo from Japan. There are plenty of videos, pictures, and articles explaining the Hobonichi system, so I won't bore you with the details. The general gist is that it is a planner, though many people seem to use it for anything but planning.
Shockingly, I'm not using mine as a planner but as a journal. I keep a log of the day's event and make note of any interesting things that I have come across throughout the day. I draw small sketches or play around with type. One thing I like to do is keep track of my focus, productivity, orderliness, etc, throughout the work-week for a month. I put a marker on the level of achievement obtained by the end of the day. The scale is from low to high, numbers 1-7. On the opposite page, I keep track of vitamins, nootropics, and other potions and elixirs I may take but were not planned ahead of time. On the margins, I write notes of the key tasks performed that day as well as my energy levels and general mood. So far, out of all variables that I have tracked, sleep is the one consistent factor that improves my creativity, productivity, and mood. For good functioning, I need 7 hours of sleep. For optimal functioning, I need 7.5. My system is still evolving and who knows what new mental territories, I will uncover next.