Seconded - I spent maybe $30 on the journal (might be a knockoff, but it works) and intentionally got one with card slots as well. No carrying a wallet required, self-contained, and when I think of something to do/search/etc it goes in there immediately.
I started with Midori notebooks in A5, and realized I love the paper, but the binding just didn't work for the way I write. Switched to Rhodia spiral bound 80gsm and haven't looked back. Wouldn't call myself "organized" per se, but far more than I ever have been and I no longer lose the random things I think of. or end up with 500 notes on my phone and no idea what's in each.