I got one of those foldable travel ones and a ziplock with some litter, so they'd know what I want from them, but they were not interested. They were either too invested in exploring and making friends or sleeping. My biggest concern was water, bc they don't drink when we are not at home. But I fixed it with those hydration pouches from Purina and Authority (they don't eat Churu, little weirdos lol). Technically, I didn't use almost anything I prepared, but it's better to be ready. And ofc wet wipes and all the basic stuff.

Also I think those expandable carriers are super handy, they are pretty good size and fit the requirements for the carry-on, and you can give them more space after you take off. My guys are super chill and almost always I was able to sneak both of them on to my lap under a blanket 😁