Blowing a tire out to the point that you can't temporarily repair it is pretty rare, but when it happens your SOL.
So........ therefore I carry a very lightweight folding spare for just such an emergency. I will use it temporarily till I can get a real touring tire. If I blow out a back tire, I will probably have to switch my good front tire to the back and put the folder on the front.
To me, this is a good compromise. The folder is inside my bags, out of the sun light, so it should last a long time.
If I ever tour in a third world country, far away from next-day-air, or on unpaved roads in Alaska, I will carry a full sized, ready to go spare.