Ah, crafting in the coffee shop is a great idea! I don't craft much in public, but every time I take a plane I take with me a cross stitch WIP, in one single colour. Once my boss took me with him on a business trip; we were in business class and when we got to the business class vip waiting lounge I didn't feel like watching tv or reading a business mag, so I just got on with my cross stitch. Dear boss was amazed that I would do that there!
By amazed do you mean the boss was embarassed, or tickled? And do you take precut peices of floss? I can't imagine they'd let you take scissors on the plane..