The hippies of the convoy did without a "chair" by using a stick as the means of taking turns to speak in the mass assembly. The stick is physically a stick or some-such that people voluntarily pass to each other (with the cooperation of everyone else in between) and whoever hangs on to it too long risks being shouted down by the mass of people who have come to the mass assembly because they know they need to make a decision and they want to hear what people have to say before they do.
In modern seminars where the speaker takes question from the audience a similar "right-to-speak" object exists: The microphone. Usually the microphone is controlled by the master of ceremony, however; he points to the person who should speak next, and the microphone is carried to the person by a helper. Note that in this variation, the audience has no way to control who speaks next. The microphone is usually not passed along by the audience, and interrupting the person with the microphone is not expected behaviour.
I have used this in roleplaying games without a game master -- we'd have a little object to pass around, and whoever had it, was the game master. -- AlexSchroeder
I've found it helps to have at least two objects, often of different colours. Alternate between one and the other. That way, there is less time wasted between speakers negotiating who speaks next as you can pass the other baton while someone is speaking. -- SunirShah