Most Useful Free Tool Ever

So I pulled one of those paper Ikea yardstick tape measure things out of my drawer today, and I thought to myself, this is the most useful free item I've ever gotten. I'm not going to lie, I have about 40 of the things between work and home and my purse, but I use them all the time. Maybe I'm just an obsessive measurer, but I love them. Anyone else care to offer up a contender for the most useful free tool ever?