It all started when I bought a warming cabinet at an auction. When I picked it up they tossed in two used 2x2's to block it up off the bed of the truck. At home I realized these were pretty nice poplar 2x2's, 8' long, and I just couldn't toss them in the firewood pile. What to do with 16' of 2x2? That sat in the back of my mind until one day I was taking down last year's calendar--aha! Puzzle blocks.
Of course you need a box to keep the puzzle in so that led to using some hickory pieces in the lumber pile (that came from another auction), and a sliding lid that came from an old piano soundboard sitting back in the corner (that I have been carting around since high school).
Our adopted Grandpa, Mr. Francis, had something he called his "seven-year pile"--things he didn't throw away because they might come in handy sometime in the next seven years. It was a large pile (and in the end a lot of it did turn into scrap) but it was also the source of parts for garden structures, kids toys, and shop fixtures. It was also a constant nudge to imagination--"What can I do with those old 2x2's?" I think we all need to have a 7-year pile of potential projects somewhere.