There were people, and probably still are, living in abandoned areas of the New York subway system. They've been run out a number of times, at one point some were given help in the way of assistance and apartments to live in.
I've seen two documentaries about this. It was amazing what some of those people were able to acomplish, litterally building houses out of other peoples trash. They had power with which they were able to watch tv on sets that other people had thrown away. Some cooked with electricity, others cooked using fires.
If you ever get the chance I would reccommend watching both documentaries.