For what it's worth, here's the US FAR on the subject:
§ 91.146 Passenger-carrying flights for the benefit of a charitable, nonprofit, or community event.
I add this because it's an example of a regulation that comprehensively spells things out. The flight referenced "to a mystery location for a classic Australian pub lunch" in this thread wouldn't qualify in the US:
(b) Passenger-carrying flights in airplanes, powered-lift, or rotorcraft for the benefit of a charitable, nonprofit, or community event identified in
paragraph (c) of this section are not subject to the certification requirements of
part 119 of this chapter or the drug and alcohol testing requirements in
part 120 of this chapter, provided the following conditions are satisfied and the limitations in
paragraphs (c) and
(d) of this section are not exceeded:
(1) The flight is nonstop and begins and ends at the same airport and is conducted within a 25-statute mile radius of that airport;
Note the PIC qualification requirement:
(9) A private pilot acting as pilot in command has at least 500 hours of flight time;