I used to use an old fashion metal luncheon tray with a piece of warm and natural glued to it, and a small roll of W&M covered with muslin stitched to one side for needles.
I don't sew by hand in the car any more, but I've fallen in love with the silicone baking sheets, everything seems to stick to them, so if I were making anew one I'd try one of those for the base material.