I like the painting flowerpots idea. We do it every other year or so as a big/little activity--the flowerpots are relatively inexpensive (think 50-75 cents apiece from WalMart) and you can use regular paint to do those.
On that same note, what about one of those pottery design studios? You can paint what you'd like, and they'll fire and glaze it for you. A good way to make a day out of something--lunch, followed by the pottery thing. It may be a tad expensive, espech for a large chapter.
What about a picnic on the main quad? That would be a way not only to advertise, but to get away from the house (and have lunch!) for an hour.
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