I'd like to chime in on the Eastern Air Shuttle while it's still fresh with other replies.

I heard that one could buy their ticket on board the plane. Later PeoplExpress did the same thing up to the mid 1980's on its flights from its Newark hub. It did so not only for BOS flights but nearly all flights.

I flew aboard an Eastern LaGuardia-Washington National flight once and flew the reverse direction later in the afternoon. It was one of the few times that I flew with no checked or carry on baggage except a briefcase.