When you eventually do get a flat, you're going to need CO2 cartridges or other pressure assist device to reseat the tire. You'll also need to carry a spare bottle of sealant. Then in order to eliminate the possibility of being stranded, you have to carry spare tubes anyway. So at that point you're carrying all the kit for a tubeless setup, plus all the kit for a tubed setup.
It depends. Some seat pretty hard. My particular setup seats really easy even with a hand pump, but yes I'd be likely to carry a of a bead blaster just in case. It would only be needed for cases where the tire needed to be demounted That is a pretty rare occurance. Most flats that aren't handled by the sealant can be plugged without removing the tire. And yes I'd carry a tube, but probably a little aerothan one. So very little extra needs to be carried if you tour in first world countries. As far as sealant. I'd use extra in the tire and maybe carry a 2 ounce bottle to get me to a bike shop if I need to add.
And don't forget many airlines require tires to be deflated for flight.
The tires stay on the bead pretty well so a non issue even when flat, plus I think 1 or 2 psi would slip by their radar as flat.