Obtainium: Any object that is found or otherwise obtained free. Coined from obtain and the -ium suffix often used in the names of elements (titanium, polonium, etc.).
I first encountered obtainium--the word, not the objects--in an article in the Escapes section of the New York Times about the weekend home of Jim McBride and Tracy Tynan--he's a screenwriter and director; she's a costume designer (and the daughter of the English theater critic Kenneth Tynan).
She started seriously entertaining the idea of a home in Joshua Tree, Ms. Tynan said, after her stepson, Jesse McBride, 31, bought a vintage Joshua Tree cabin, a renovated shack constructed from what’s called “obtainium” (found objects). Enticed by desert beauty and the possibility of an inexpensive second home, Ms. Tynan focused at first on buying land with the starry sky above and gave little thought to building anything. “For a while, I was obsessed with Airstream trailers,” she said. “I even took Jim to a trailer park in Palm Springs to look at a very funky Airstream.”
(That article also introduced me to another interesting word, monzogranite. According to Wikipedia, monzogranites are biotite granite rocks that are the final fractionation product of magma. I've been to Joshua Tree--yes, it's as weird and wonderful as everyone says--but had never learned the word. Monzo- derives from Mount Monzoni in the Italian Tirol. View monzogranite photos on Flickr.)
Obtainium Technology Recyclers owns the obtainium.biz domain. The misleadingly named Obtainium Performance Products makes titanium springs for mountain bikes. Obtainium.com is parked--make an offer! And this interesting page gives lots of suggestions for finding house-building obtainium--in the U.K., anyway.