While dangerous as hell, and illegal in lots of places, the shoulders of interstate highways. Folks have a flat at night, unload the trunk, put on the spare, throw the flat into the trunk, and often forget to reload their stuff in the trunk before they drive off. I have found bag phones (back when they were in style), wrapped Christmas presents, lots and lots of tools, you name it. (and yes, I turned the stuff in, or at least most of it, per departmental policy)...