A few years ago I took a USAIR shuttle 727 from LGA-BOS and back. On the BOS-LGA return trip, I was hanging around the gate waiting. I think it was mid-day and there was almost no one else around. The FE came by and noticed I was interested in the plane. He asked me if I wanted to come to the cockpit now and "help out." I was very excited (obviously). Once on board he let me start the APU and a bunch of other things.