5mm (cheap) A4 Pad on my desk and a pen - nothing important/with duration longer than a day or two goes in there (but I write the date at the top right of each page and keep them on a two month sliding date window), I tried taking a photo of each page but realised I never looked back more than a couple of months so just stopped bothering.

Everything else I just throw around on the filesystem wherever makes sense for the thing I'm doing.