Do a full circle tour of the Yamanote line (or get through as much of it as you can), getting off the train at each station (without exiting the ticket gate) and explore the insides if the station. You'll only need about 5 minutes for a place like Uguisudani, but allow an hour or so each for the bigger stations like Tokyo, Shinagawa, and Shinjuku. You won't lack for places to eat, just the time to try it all.

You'll get to interact with plenty of people along the way...