If the tour is long enough, you will probably need to adjust and replace brakes. You may need a new chain along the way, but you can probably acquire it en route. You may need new tires, and good ones are harder to find en route. You may need new cables. Carry an extra tube or two as not all flats are patchable. A FiberFix can fix a broken spoke until you get to the next bike shop.
I carry a cassette removal tool, but have never used it on tour. I carry chain repair tools and parts, but have never used them on tour. I'm sure many others have needed them. It's just a probability game. Everyone gets to make their own trade offs of weight and risk. And there is always anxiety involved in making the choices. When touring with others you can share the load, so you can take more.