I sketch where ever I can find a free model, usually human. Such models do not know that they are being drawn and do not stay still for long, so the sketches have to be quick, at most 5 minutes. I use an A6 sketchbook from Rymans, a mechanical pencil with a 0.7 B or 2B lead, which easily fit into a pocket.
The aim is not to produce a picture, but to check that the eye has seen accurately, and to build up a store of images in my mind, that I refer to when carving a human figure. I sketch and carve the human figure, as humans are the animal I see most frequently. The aim is to do one a day, as advised in all good drawing books, but this is not always practical, however over time the average works out..
I do not refer to the sketches after they have been drawn, and when the sketchbook is full, it just goes into the box with the books filled in the last 40 years.
Sketching on a moving bus has the advantage that the model stays in the same seat for much longer than they do in a cafe. It is amazing, however, how many times they move their heads and hands. The disadvantage is the jolting of the bus and the difficulty of actually drawing.
We went on a coach trip with Todmorden U3A to Hutton in the Forest and these sketches are of members of the party waiting for the coach back
At The Dog Show. I sketched one organiser in all sorts of different positions as she waited for participants to come to the Agility contest. I also caught the professional photographer and some contestants