Probably pop across the Pacific?
There were 2 x PA28 flying in convoy a few years ago on that route. One had engine failure. The other stayed overhead on station as long as he could but that-I think-was that.
When not using UPS or Meccano Mail, I would rather, as the ferry pilot, have an extra 75kgs of fuel, food, water or an extra ELT than a supernumeray crew member, especially one who has no previous experience of ferry flying.