Here's an opportunity to get out and take photographs outdoors. This won't be a formal meetup, per se. Just go to the event and enjoy the spectacle. What makes this an interesting venue is that photographers can walk around the balloons and get candid shots of the folks preparing their equipment. So, while it isn't really renegade, it's the kind of atmosphere a renegade photographer looks forward to in order to capture events as they unfold.
The details of the event can be found at http://www.ballunarfestival.com along with the detailed agenda.
The mass liftoff looks like it would be around 5:00pm on Saturday.
Admission to the event is either $10 if ordered online, or $25 at the event.
Here is an announcement for this event from the Houston Portrait Network meetup group:
The discussion on their meetup site has some good tips on how to photograph balloons, and more.