I've been journaling more or less continuously since 2003 by simply writing short timestamped entries about whatever ideas or notable stuff there is going on at the moment. There's pretty much no index beyond this, and being just about as simple as possible is what keeps the habit going. There's currently around 4M of plaintext in this journal.

Since I started using org-mode, I also use the org-mode clock-in feature to track time spent in various programming projects I have, both as a way to keep me focused on the task and as a project tracking tool. The project files are otherwise pretty much similar lists of time-stamped short entries as the general journal is.

I've tried to do TODO lists several times, but I always end up not maintaining them and then clearing out the months out of date items much later.

I've had some specific systems for tracking sleep times and running times using org-mode's spreadsheet feature, but I haven't maintained any of these nearly as consistently as the main journal.

So a complex front-loaded system doesn't seem to work for me nearly as well as a free-form thing. I wonder if there was a way to track quantitative data using a lightweight markup in the main journal instead of setting a burdensome separate system for it, so that it could still be recovered using some sort of clever parser afterwards.