I carry a spare tire on most tours. Not a replacement comparable to what I am rolling on, but one good enough to last at least a few hundred miles to get to a good bike shop. And two tubes, with some self adhesive patches.

With 26 inch tires getting rare, when I tour on one of my 26 inch bikes I most certainly carry a spare.

The 26 inch one I use as a spare is a light weight mountain bike tire with not much tread, folding bead, 47mm wide, 430 grams. When I tour on 700c, I carry a folding 33mm wide cyclocross tire, 290 grams. These might not last as long as my tour, but would at least keep me on the road until I can buy a good tire.

A month ago the tube on my errand bike got a puncture. Patched it. Couple days later rode that bike to the gym a mile and a half away. When I came out of the gym, the tire was totally flat. My errand bike rarely goes more than five miles from home, I do not carry a spare tube. Walked the bike home. The tube had a 7 or 8 inch long split. Part of the tube was a bit too thin from the factory and from the looks of that split, I am sure when it deflated, it was likely quite loud.

Two years ago on a tour with a friend, he had brand new tires with a lot of puncture protection. And he put in tire liners to make sure. Day three, he had a tube split along a seam in the tube. Down to only one spare.

That is why I always carry two spare tubes on a tour, even though most of my tours do not even have a single puncture. It is like buying insurance, you hope you never need it but do it anyway.