I keep story ideas / research in many places. There's physical stuff in notebooks, single pages, 3 x 5 cards, loose sketches and sketchbooks, newspaper and magazine articles scribbled-on in the margins, and printed docs. Enough that I have three of those big clear plastic utility boxes from Home Depot just filled with story notes.
I've gradually been digitizing them, so they can join the large numbers of Word files I have of slightly-more-finished stories.
I keep a lot of stuff in my head, but recent memory issues with friends (and the fact that I'm pushing 50) have made me aware this is not secure from loss. So I'm trying to at least type out additional notes for projects. I'm not completely joking when I say it's for my heirs, all of whom write, too.
Journaling taught me to write notes - they can always be strip-mined later. I'm finally making money off ideas I first wrote down two decades ago. Some of it is for a huge story arc I've been playing with as a hobby for years. Some is for one-off pieces. In most cases, the idea was better than my writing skill at the time, so I had to catch up.