Feet are always a good option on a streetcar ride. I live in Toronto some of the time and I find Torontonians fairly insular. I guess you have to be in a big city in some respects. This insularity allows me to draw just about anyone travelling on the streetcar. Readers are the best, they don't move so much. Occasionally no one's reading and everyone is just sitting, looking around. The minute someone figures out you're drawing them though they get all self-conscious and start moving around as much as possible. This is where feet come in. No one cares if you draw their feet (hands apply here as well but don't stay still as long). So when there are no likely candidates for faces I draw their feet.