EhBC has an excellent description of what goes on:
" There are three reasons why we meet in a public place.
1.It makes us easy to find.
2.It gives those who might be interested in joining us a chance to look us over first to make sure we're not a bunch of strange, scary people (don't laugh; first-timers can be easily intimidated).
3.It helps preserve everyone's anonymity, which is important to many people.
Keep in mind that these munches are just friendly social get-togethers.
Everyone wears casual clothing, though if you want to wear something more elaborate nobody will object.
You may be a submissive, but you are under no obligation to behave submissively to anyone unless you choose to. You may be a Dominant, but you have no authority over people you may meet at the munch.
Treat everyone the way you yourself expect to be treated, and you'll do just fine."
Many thanks to the EhBC group for that description, they have a comprehensive calendar of events if you are looking for more activities.