Back in college, '90... on two occassions I was the only pax on a turbo prop, for Eastern (or whatever their little puddle jumpers were called) flying from EWR-MHT, last flight of the night. Had the same FA both times.
Both times I got several cans of soda and bags of honey roasted nuts.

Years ago, I was only pax on a...DC9? Something smaller. BWI to IND, I think.

Early morning flight, I was NOT only person in gate area, but I sure was the only person to board. At the time I was a midshipman at the Naval Academy, flying in uniform. FAs converged on me, brought me up to F, for my first-ever flight in first, and really took care of me. Was brought up to the cockpit - remember THOSE days? - to meet ex-Naval aviator driving the bus that day.

And back then first was pretty nice. Sigh.

1 other revenue pax
 

In 2004, I flew a UX CRJ from IND ro ORD. There were two revenue passengers, myself and one other, and a deadheading pilot from another airline.
Because of weight and balance restrictions, the three of us had to be seated in rows 12, 13, and 14 or something like that.