Below, I’ve quoted a comment I wrote last year on kbin (RIP) about what I keep in my journal.

I started keeping a daily journal about 10 years ago. It’s helpful for tracking what I worked on as well as various health issues. I skim through it once a week before talking to my therapist and read all entries from the past year when I need to prepare documentation for my annual performance review at work. I’ll grep through the whole thing occasionally when I’m trying to remember when some particular event was. (I don’t do that very often, but it is handy when I need it!)

I typically track:

• current date for the entry (both in the file and as the file name)
• date and time I wrote the entry
• when I went to bed
• when I woke up
• health issues (if any)
• what I worked on (professionally and for my hobbies)
• places I went (if anywhere)
• significant conversations (particularly if there’s something I need to follow up on)
• what I’m watching/reading/playing/etc.
• anything else that seems noteworthy

I keep my journal in plain text files named like YYYY-MM-DD.txt. Right now it’s all in one big folder. I have it in version control and back it up to various places occasionally. I’ll probably split it so there is a folder for each year eventually.

I started doing this after someone came up to talk to me and I realized that I’d recognized him from a particular place a few years earlier but could not for the life of me remember his name!

A notable change since then is that I’ve augmented the journal with a set of weekly “time card” files where I jot down a few words about what I’m doing each day as I do it – super useful for preparing summaries for my boss on what I got done each week, and it’s helped reduce some of my anxiety/depression problems. I keep that as a set of conceptually related but separate files. To be clear, I make those for my own use; work doesn’t require it, and I don’t share them verbatim with anyone. They’re just another tool to help me remember the things I want to make sure I don’t forget.