I had some great fam flights before 9/11 spoiled it for us. If you booked with someone like Britannia (aka Thomsonfly) you were guaranteed the jump seat so they could still sell the seat in the cabin which you would otherwise occupy.
One flight, Gatwick - Malaga with BA, we were just starting descent into Malaga; I was positive I heard ATC clear us to descend to FL110, captain was on the cabin PA and I heard F/O readback FL100. I thought I'd better mention this so F/O asked the captain (who'd been pre-occupied); he asked ATC who said 'FL160' in a rather terse tone of voice!(ie emphasising the '6')
Captain remarked 'that sort of thing often happens around here'.