In a given public situation, especially where you and others are in a enclosed, even confined space, imagine an emergency or disaster (small or large) that requires you all to stay and even work together for period of time you define. There’s no one else, just you and them. Maybe remote contact via cellphones or other devices (outside or within your group), maybe not. Write a list of one or more scenarios. Look around and catalog these fellow travelers, then write character sketches in the context of those scenarios. Avoid cliches, or at least the obvious cliches. Try to avoid heroes and victims.
It could be a restaurant, a dinner with friends, a wedding, a market or store, a library, where you work or go to school. If it’s a store, maybe it’s a mundane location like a supermarket, maybe it’s a sex toy shop. What if it was up to you and the other “perv’s” to save the world? (Yeah, “perv’s” is a judgmental joke here.)
I do this exercise at least once a week during my bus or MAX train commute (and whenever I visit a sex shop), sometimes mentally and sometimes in my notebook. (It makes the sex shop staff think I’m a cop.)