We'll start with introductions (name, what you do, who you work for, why you do what you do).
Next up we'll find out what everyone has been doing recently (what projects have you been working on, have you been having any issues anyone can help with?).
Then we'll break into our normal conversations and this is when we generally drop into separate conversations about specific topics.
Because this group has a large variety of specialties and interests we usually don't have specific topics.
Bring business cards since they generally come in handy.