Back when I finished school in 2002 I went on a backpack trip with 2 very good friends. We traveled through western Europe (Ireland, Scotland, Spain, Portugal) by train. The train ticket called Interrail allowed us to take basically all traines we wanted to.
During the trip we calculated with 15 euro per person per day. This money was for everything, Hostels, camping sites, food, booz, public transport in citys and entry fees etc. It was interesting to see on how low budget you can get along in western Europe if you focus on it.
Living without money in a well developed society is hardly possible if you do nt choose to live outside of the society.