To add to the experiences brought up, I quit carrying spare tubes. When I carried some, I never used them, as patching a tube on the spot added minimally to the whole recovery operation. You anyway spend time examining what happened to the tire. Moreover, I ride bikes with tires in the range 16-29", rotating at times even during a day and remembering what tube to fetch is just too much - the patches are always the same and packed, in my case, together with the pump and ready for grabbing.