There are few guarantees in life. In fact, there’s only one that is certain, so it’s a good thing to enjoy triking while you still can. But with all the talk of superior tires, tubes, and liners, can a flat still happen? Sure, anything is possible, like you could be coasting down a steep mountain at 50 miles per hour and not see a sharp piece of metal that slices right through everything like butter, whether you have the best gear or the cheapest. Or a Martian could land in the path of your overland trip and melt your tires with its ray gun. But these things are not likely.
What is more likely however, is a small sharp nail that you hit just right and it penetrates through to the tube’s air supply. You could just put in a new spare tube, but you didn’t bother bringing one due to your confidence that you were immune to flats altogether.
Consider this: Minimal intrusions by sharpies can be repaired right on the highway, by using little tube repair kits that take up practically no room at all (like the one from Park Tool). The job goes relatively quickly, and if done properly, which is pretty easy actually, the repaired tube will be as good as it was prior to the little hole that allowed all your air to re-enter the atmosphere. So really, this is the fourth level of protection against flats. Be ready for almost anything before your trip, and ride in triker’s bliss. Remember this motto: Failing to prepare is preparing to fail.