Most of my local trips are two people.
Almost all of my cross countries have 2-3 people, plus one of the following:
1. One of two dogs. We haven't flown with both dogs yet.
2. Enough luggage that you would think we were on the road for a month
3. Enough camping gear to survive OSH in style. Large tent, multiple cots, etc, etc.
4. Pilot & Paws crates - two medium size
Running LOP you can get the economy of a two seater, but you have the room to haul significantly more.