Personal choice. Some campers really get out into open spaces that either don't have phone/cell service or emergency services won't travel that far off the road so they carry a complete spare, rim and tire. Others just carry the tire and use their ERS to install.
My one flat the tire guy arrived with a replacement that was the size I needed. Price was a bit more than I would have paid if I was shopping around but that can be difficult on the side of the road on a Friday evening. Removed the old and installed the new all in about 10 minutes. Delay my outing by maybe two or three hours overall. ERS paid for the service and trip charge while I paid for the tire. Just part of the ownership experience.
If you do carry a spare just remember even though it isn't mount it still is aging and won't last forever. At some point you'll need to replace it even if it was never used. At what age, I can't say but I would suspect it might last a bit longer stored in a cool, dry place.