Gather a group for a carwash. If you don’t have access to water, offer a full-interior cleaning and vacuuming instead. Have everyone involved wear the same colour T-shirt or ones with your charity’s logo. Talk to your town hall; they might allow you to use municipal land for a central location.
Host a series of cooking classes. Volunteers can take a turn teaching participants how to make a favourite dish. This idea combines well with the charity cookbook idea (above).
Kids love to have their face painted. Have a book of patterns on hand; it helps narrow down choices. This idea works well with any of the tournaments noted above.