A munch is simply a group of folks getting together, generally at a restaurant, to share a meal and get to know one another.
Sometimes folks will continue the time together after the actual meal with other things...wandering through the area if there are shops/sites to check out, etc. What does or doesn't take place after the meal is normally determined by the host(s), the weather and the location. Joining in activities after the meal, as with the meal itself, is optional and up to each person to decide for themselves.