Instead of listening to music, they could be looking at the other people on the sidewalk or mulling over private thoughts. I have used it only a few times, to see if it was working. I have never walked along on the sidewalk with it held to my ear. I suppose the cell phone is part of the information revolution that holds great promise for us, but no one has ever demonstrated any addition to productivity resulting from the availability of cell phones. I have been told that the use of water bottles has something to do with the cult of physical fitness.
Physical fitness requires the intake of lots of fluids.
But those fluids could be taken at home, from the kitchen faucet. Anyway, many of the people I observe do not look as if they were devoted to physical fitness. And still they hold on to their bottle. Maybe that's the clue. They want to remain in, or return to, their infancy, when the nursing bottle was the cure for all discomfort and anxiety.