2mm squared graph paper (A4) and a decent biro. I write the date at the top right of each page (in ISO format as god intended) and when I'm done with the page

2mm squared graph paper (A4) and a decent biro. I write the date at the top right of each page (in ISO format as god intended) and when I'm done with the page it goes on the pile. That's as complicated a note taking system as I've ever needed, if I need to find something I just flip the stack looking at the dates until I find what I want - requires no structure beyond that - in the very rare case I can't remember the date even roughly I have to go through the whole stack but that's rare since I normally have a date on an email, ticket/slack conversation to get me in the ballpark.