I’ll scribble anytime, anywhere, me. I only had a lined notebook with me but what the heck! It’s good practice to draw quickly, you can’t expect random people to stay still and pose. It forces you to identify the basic features of your subject and reject anything above and beyond that.
I am putting my series of drawings of ancient Welsh monuments on Artfinder. If you want to buy one, you can see them by clicking on the image below or the Artfinder link at the top right of this page.