A slightly-larger-than-A7-sized pocket notebook that was 50p from Asda. The pages are quite small - 50-ish words/page. I had a bit of stuff backed up in my head to get down - not quite mindmapping, but some looping through thoughts about thoughts and some sentences being followed with a paragraph of caveats. I've just counted pages, and I filled a quarter of it, not a third - 19 pages out of 80, single side. I keep it in my jacket pocket with a pen, though I'm largely home for the next week or two so should keep it closer to hand. I don't actually do anything with the notes as yet; presumably one day I will type them up. Just getting it down helps clarify my thinking, though.