We have had excellent results over the years by doing wine and beer tastings. Where possible and practical, we ask participants to bring bottles from their states/countries/regions. Same as happy hour, but with a theme or sorts. I've done this at least 6 times at tech conferences and it helps create extra buzz when those who are into either beer or wine chat about it online in advance. At least one person who knows enough about the "topic" should ensure quality and diversity, if possible. We make it clear that people are not obliged to consume or contribute to be a part of the event.
The event is always put near end of day, obviously and carries a couple of gotchas: if you're in a hotel, they will often not allow alcohol from elsewhere. A venue must be found that can both supply glasses and is ok with external drinks. Usually this has a fee associated with. Once I even simply offered a woman in change $50 to bring in a supply of glasses, and she was happy to accept. Situations vary a lot, though. You'll need finger food for this, as well.
We've found these to be really well-liked by attendees of all tech conferences and they can even learn a little geeky stuff about what they're drinking.