One long group activity is hard. We did an open house on jobs. We had a 5 minute powerpoint opener, but the main activity focused on a large map we made on the floor where the students had to follow direction cards pulled by the teacher (go left, go forward, go back, go right). After pulling three or four cards, the student would land at a hospital, a dentist's office, a police station, a fire station, etc. Then the student would have to announce who worked at this place and answer one question about what a fireman did for his job. I know this isn't exactly what you were looking for, but maybe it will help spark an idea.