The Simple Dollar cover everything you need to know about using a pocket notebook.

It’s really hard to believe, but I have to say that one of the most – and possibly the most – profound changes I’ve made in my life over the last several years was the simple decision to start carrying a pocket notebook and a pen with me wherever I go. Unless I’ve made a mental miscue when swapping out a finished notebook or something, I do not leave the house without my pocket notebook resting in my hip pocket or my shirt pocket, with a trusty pen right there beside it for jotting notes.

— How to Use a Simple Pocket Notebook to Change Your Life by The Simple Dollar

If you don't have one, get one. Keep it on you at all times. It's more of an asset than you think.