When you're building weird stuff out of car parts (or if you rely entirely on cheap-ass beater cars for transportation), you'll be spending a lot of time in your local junkyards. I've always loved junkyards anyway, so I'm often at my favorite yard, sniffing through cars like a junk-food-mad bear digging through campground dumpsters...
In addition to car parts, you can also find interesting objects left behind in cars by former owners. For example, these campaign buttons for past California gubernatorial races. The guy on the left is Abe Tapia, erstwhile head of the Mexican American Political Association and candidate for Lieutenant Governor in 1978; on the right is a Dennis Peron button; Mr. Peron ran in the Republican primary for governor in 1998, on a platform centered on the legalization of marijuana.