>> Terrific local volunteer organizers Greater DC Cares are hosting a happy hour tonight at Mackey’s with what looks to be free or deeply discounted beers provided by sponsor Samuel Adams. 6 to 8 p.m. Non-volunteers welcome to attend and learn more about the organization. >> The Lost Bayou Ramblers bring their Cajun dance music up from Louisiana for a free concert at 6 p.m. at the Kennedy Center Millennium Stage. >> Black Cat,…