do you mean something like:

  * bullet journal https://bulletjournal.com/  
  * analog https://ugmonk.com/blogs/journal/analog-the-simplest-productivity-system  
  * hipster pda https://en.wikipedia.org/wiki/Hipster_PDA

or do you have your own system?

i use little index cards on occasion, but i often forget to bring them or later archive them.

i bought an s-pen so I can scribble notes in a handwriting app, next to tiddlywiki (and now also obsidian) managing markdown and org files (the letter linked to markdown otherwiste tiddlywiki doesn't get it) see how that goes.