You did reserve PE in advance, and they had a printout of "confirmed" reservations that they checked off at the gate.
$19 flights EWR-BUF and EWR-BOS were a part of my courtship of Mrs. Transportprof, back in the day.
I never did the flight to LGW, but I believe that you could buy a bottle of Dom onboard for $50 in 1982, or thereabouts.