Global Feedback, an organization that seeks to reduce food waste, has held public eat-ins since 2009. At these events, dishes are prepared by well-known chefs using ingredients that would otherwise have gone to landfills. Next week in Union Square Park, some 5,000 people will be served by chefs like Dan Barber, Jason Weiner and Evan Hanczor, who will also show how to use the ingredients. The organization promises to feed another 5,000 New Yorkers in need: Feeding the 5,000, May 10 from 11 a.m. to 4 p.m., free, feedbackglobal.org.