I love to have handwritten notes, it gives me the chance to organise my crazy ideas or to list the solutions I think will work. Since I can get distracted easily, going back to my notes helps me to get back on track. I also have a nice small notebook with grid pages, so it's fun to doodle pixel art there.
Fun fact: When I was in college I was too tired to keep coding, but I left myself a note before I went to sleep. The next morning when I woke up I reviewed my code, I was afraid it wasn't working until I saw my note from the night before... and that saved my project! (Thanks Tired Me™, you were always reliable!) haha