One of the difficulties I have with doing a Sketch Crawl is the fear of trespass... even in a public place. I usually feel that if it's a retail outlet, I should either be there to buy, or at least to be browsing. It was as a result of being a two-some in our 'crawling' that emboldened me to stand in a narrow aisle at Joe Euro's Wine Seller in Port Townsend yesterday, whip out my little Moleskine and pens, and sketch away. Still, I only got the bare outlines and basics, memorizing the way the light glowed and the difference between the green hues of two of the bottles as well as the brick's shadow tones, so to be able later to fill that stuff in. I had some help with the foil and label on the Roederer bottle by checking a British Champagne importer's images online.
I have to say, sketching on the fly, and leaving more to memory later, has certainly helped me to see the details of the world more comprehensively.