Here's the event description from the San Antonio Convention and Visitors Bureau (I couldn't do a direct link; just go to the site and search the Calendar of Events for things going on June 24, 2007):
Picnickers will have a brown-bag ’’absurd sandwich’’ exchange. Sandwiches include; Open-faced pickles and sauerkraut on rye, peanuts, grape nuts and Nutella on tortillas and a Cookie Fluffinutter. They will then delve into meaningful readings from the San Antonio Yellow Pages. Audience members may be asked to participate at any time. Water will be served to anyone who brings a vessel. For information call 210/882-8094.
Sounds like fun.