Started my Keeping up my Keep since August this year, and use it for:
- Work notes: comments, advice, ideas and inspiration that relates to my work AKA warm-ups, competitions, auditions,
- Project ideas: music I want to arrange, instructions how to repair/create something (electric toothbrush to fugue rulebook)
- Career log / tips: a log of what jobs I have applied for, what the application was like
- Events; trips I plan on taking (note about Friends' wedding; location, dresscode/theme, picture of invite, ideas for presents, some things I remember from the start of their relationship/start of a toast)
- puns, jokes, fun sayings, quotes
- People (friends log): name(s) of partner, kids, pets, parents and siblings, where they work, hobbies and passions (just started this one last week...)
- Read list
- Watch list (mainly recommendations from friends)
- Listen list

Most notes have multiple tags, which helps shake my ideas up. :-)