Tea! Best team I ran stopped at 4 every afternoon for tea and we all decamped to the boardroom for a cup of tea and a chat. It is amazing how much productive cross-pollination went on. We bonded too and an informal rota for tea making and cake buying emerged. We did it for almost 7 years and were known across the company for doing it. We even went as far as inviting interviewees in for tea once they had gone through the formal process so we could take a look and get an idea of their suitability.
As a result we were a much more cohesive team. The only people I lost were through forced redundancies. We did some really great projects and worked very hard, but it was fun. I am still in touch with most of the people from that period of my life.
Some of us extended tea to beer - outside office hours of course. We worked in central London and the local pub was often a place where the office politics got worked out.
Edit: I missed out an important thing. We had huge whiteboards on the walls of the tea/board room and we'd put difficult problems up which would get solved slowly and thoroughly through group effort. We had one board which stayed up for almost a year as we all worked on software around it. It was a really good way of sharing intelligence and expertise.