It's not always easy to find a good block of time to sketch. Going to the beach with the family gave me ample time to draw. The other advantage is that there are plenty of people around and nobody seems to bother if you are sketching.
You have to be quick and there are times when people will move. It will happen, and in this case I just start a new sketch (on the same page if the first one is not too advanced, like below). The trick is to start by drawing the people first and then the objects that are less likely to move.
For speed and freshness, I draw directly with the ink liner, without any pencil outline.
You can click on each of the pictures to enlarge it.