What is the definition of "occupant" in 14 CFR 91.307?
If you're solo you don't need a parachute (emphasis mine):


  Unless each occupant of the aircraft is wearing an approved parachute,
  no pilot of a civil aircraft carrying any person (other than a
  crewmember) may execute any intentional maneuver that exceeds [...]


Incidentally, 91.307 says nothing about aerobatics; that's in 91.303.

And this question is closely related.