And, no, the answer is not podcasts!
@jason they already sell soda and water and candies on the trains. Why not take it a step further and sell what everyone really wants? 
@Gotterdammerung my thoughts exactly.
@jason
I respect those hustlers on the public trains, especially the Metro Blue Line here in Los Angeles/Long Beach. Always reliable or a cold drink on hot days. But I never saw anyone sell liquor or contraband. Probably too risky considering? 
@jason How about knitting?
maybe they didn't mean LISTENING to podcasts, maybe the answer is RECORDING a daily podcast on there
@sydneyfalk okay, now THIS is intriguing to me!
I'm thinking of selling liquor on the bus to other weary transitors.