Well, as soon as Katie sees the carrier, she loses her appetite, whether she's just going to the vet or going on a trip. She's flown from LA to Hawaii, from Hawaii to Texas and from Norfolk to here and never once gone to the bathroom on any of those flights. She's been on long car trips, too and just would rather hold it. Maybe you could get a small cardboard half box (like muffins come in, but small enough to put in your carry on) then carry a sealable bag with clumping litter in it. When you stop in Lajes, see if he wants to go, then either scoop or throw the whole thing away. Sounds a little gross, but when my kids were babies I carried a lot of gross things around, then, too LOL.
I usually put down a towel, then a shirt I've worn to sleep in for her to lay on. That seems to comfort her a lot. Hide some treats and either get one of those hanging bottles of water or a small sontainer you can refill if you need to. If you think your kitty might pee, I would just pack extra old towels and some sacks to put them in if he has an accident. Vets can sometimes give you a kind of kitty tranquilizer you may want to ask about. It doesn't knock them out, but they will be more calm on the plane trip. Some people don't like the thought, so it's up to you. I've used them and she had good flights, but since she's getting older I may skip it this summer.
Hope this helps!