I’ve travelled with Otto for 5 hour trips a few times, and this winter we’ll be doing 8 hours. I’ve never had a problem!
K&K gave you some great tips. I would add to make sure you line the bottom of the carrier with a lot of absorbent materials. My bun pees in his carrier ever single time, and if I don’t have enough to soak it up there’s a huge mess and he spends all his time trying not to sit in it. He doesn’t seem to have that instinct that dogs do to not pee in a small space. I use newspaper, covered in paper towels, sometimes a piece of fleece, then some hay in the back.
I honestly wouldn’t worry about water too much for a 9 hour drive. I would offer it a few times during stops, but I wouldn’t attach it to the carrier – water bottles leak like crazy in the car. Honestly, my bun will go 15 hours at home without taking a drink (and as humans we can easily go 9 hours as well). The problem with water is it often gets all over and makes a mess if you leave it in while driving. This will be much more uncomfortable for him than having to wait a few hours between rest stops. My bun won’t even drink during rest stops anyway. I would put some nice veggies in that he can eat if he feels the need for some water. Something like romaine lettuce will hold a lot of water and keep him hydrated (if he needs it) without making a mess. K&K’s syringe idea is good too, if your bun will put up with it.
I would give hay and some veggies, but save the pellets til you get there. He won’t miss it and they’ll probably just roll arond and make a mess.