The less formal, the best. Because that's exactly what the intent behind it is: the equivalent of a team's gathering about a cup of coffee/tea/water/anything to

The less formal, the best. Because that's exactly what the intent behind it is: the equivalent of a team's gathering about a cup of coffee/tea/water/anything to discuss/chat about the mood of everyone, and the quick status of their work. Alas... in most of the companies I met, it's become a rigidified strictly business ritual.