Full service gas stations used to be the way of life in America. Now it is rare to see them anywhere outside of New Jersey. Bring back the service, even if just for a day, to a local gas station. Find a gas station that is willing to help your group out. Have your group become gas station attendants for the day. For a donation have members of your group pump gas and clean the windows of all the cars that come into the gas station. Most people will be more than happy to let you help them. Gas stations provide the squeegees, cleaning solution and paper towels already, so you will have all the equipment you need. You could ask for a set amount, but most people will be more generous if you just tell them to feel free to give whatever they would like. Make sure you advertise locally to improve your turnout.