Doing laundry can be expensive. Buying a bottle of water from a machine is ridiculously costly. Actually any coin-operated machine will likely cost more than you would expect. Surprise others by springing for their wash or beverage or other automated expense. Leave a few quarters near the coin slot of washers, dryers, or other machines, or collect a number of quarters in a plastic sandwich bag and leave it with a "this one is on me" note. Quarters can make someone's day!