I always try to put my personal assumptions aside and buy the person a meal - in the UK a lot of convenience stores have "meal deals" on that cost around £3 for sandwiches, a side and a drink. I usually go with that without asking them first, and then listen if they want to talk.

I think the worst thing about being in their situation would be that most people wouldn't listen, and sometimes that can be just enough to get you through the day.