Years ago I had surfed across a shopping cart documentary on cable TV.
Apparently it is now available to be viewed online.
http://www.nfb.ca/film/carts_of_darkness/
Carts of Darkness is a Canadian documentary that follows a group of homeless men in Vancouver.
They use shopping carts (presumably stolen from local retailers) to gather cans and bottles in order
to collect the deposits, and to transport personal belongings. They also use them to engage
in a series of impromptu shopping cart races down some terrifyingly steep streets.
If you ever found a shopping cart abandoned in some oddball location, the story behind it is
probably something similar to this.