I feel like the act of writing down things on paper is becoming way to buzzwordified. Personally I just write notes, todos, calendars etc down on a college notepad, no need for all sorts of supplies or fancy notebook, and no need to subscribe to any one religion of how to do it.
Find some paper, find a pen, write stuff down. Keep it simple.
I have adopted one convention: If I need to act on something later, I put a box to its left. Once I acted on it, I tick it off with a checkmark.
For example, during I a meeting I realize a problem in our software which is unrelated to the actual meeting agenda. I jot down a box and a few words in my college notepad. Later, when I have a few minutes, the "few words" are expanded into a proper ticket in our issue tracker and the box is ticked off.
I strive to tick off every box in my notepad by the end of the day. Sometimes that just means writing it down elsewhere (Email, electronic todo list, OneNote, Jira, etc).
I do something very similar to this. I put a box to left of action items, but instead of checkmarks I put '/' if it's in progress and then 'X' when it's complete. This allows for quick visual scans of what things still require attention.
For anything I run into that's a problem (gotcha, bug, mistake that requires a task to be re-started), I mark with '*' in left margin. This makes it easy for me to quickly find it later.
For things that are super important, I draw a box around the whole entry.
I'm also very conscious to keep things very brief and intentionally obscure (don't write last names and never write customer names), to avoid potential problems of having any sensitive information leaked. If I'm working with Marty McFly of Acme Inc. on a joint project Time Travel v2.0, I would only write things like 'respond to Marty concerns'.
This also works for me as well. I use a physical logbook at work (some customers don't allow unauthorised electronics). Actions that come my way get marked with a circle. When I get some keyboard time I try to execute the action immediately or add it to an electronic TODO list, and in either case put a big X in the circle.
It is indeed simple and effective and doesn't require any tooling.
I use a pink and green marker. If I put a pink splodge on something it needs attention, a green one next to it means "dealt with". Makes it very quick to skim through documents and see if there's anything I've not looked at yet.
Find some paper, find a pen, write stuff down. Keep it simple.