I sometimes carry a spare tire when I'm touring (on a multi-day trip away from home) on my little-wheeled Bike Friday because it's unlikely that I will be able to find a suitable replacement on the road. It really depends on where I am touring and how long I am willing to wait for a new tire (via overnight delivery from a shop that carries decent 406mm tires) if the unthinkable happens and I can't ride at all on my existing tires.

I only carry tubes when I'm out on day rides. I figure I can always use a dollar bill to boot a tire, and I always carry some cash with me.

A work colleague of mine does carry a folding tire with him. He rides very skinny tires and is more comfortable with an extra tire in addition to his tubes and patch kit. He uses a folding tire and stashes it in his CamelBak.

--- Denise