I'm flying home today. The trip will take twelve hours. This is just a bit too long to go with one diaper, that is, without a plan for a change during the trip. I'll have a one-hour stop between flights and will change my diaper there. I'm bringing that spare diaper, and another one, in my carry-on. In addition there are two in my suitcase, in case things go wrong.
I'll wear a terry-lined plastic pant over my diaper. And I'm wearing Dry 24/7's for the trip.
I bought some Depend diapers from a pharmacy here, before I decided to order some good diapers and have them sent to the hotel - I've been here a month. I have considered stuffing a Depends inside my good diapers, then removing it during the trip, but that would leave the good diaper sagging. So I'll change in an airport bathroom stall.
I once changed in a moving bus, in the cramped bathroom. That was an adventure! Traveling in diapers is a matter of logistics, and only needs a bit of planning.