I really really like index cards for general note-taking/reminder/to-do list purposes. Scraps of paper get ratty/mutilated/lost in a hurry, folded sheets don’t get unfolded (I mean, in a pinch, you write on the outside and you’ve got yourself a field-expedient index card, but…)

Also, my to-do lists can be very… diverse.

I think one time I left behind at work for my co-worker to find a list combining:
-a fairly detailed order-of-battle for an amphibious invasion I was planning in Hearts of Iron.
-a reminder to buy socks.
-FIX PANTS.