You should talk to the person sitting next to you. I find developer meetups great fun. I've never met anyone there who compared the size of their GitHub repos! You can get to meet a whole range of people, and if there's an interesting talk and free stuff that's a bonus. Pretty much all of the time we talk about other stuff, where we work, our bosses, the local news, philosophy, bitcoin or whatever - it could be me, but we hardly ever talk about the specific topic of the night.

The hardest bit is when you don't know anyone else and have to break the ice on your own. But the next time there would probably be someone you met the first time...