If you keep him in his kennel for the length of the trip chances are he won't pee in his crate. Dogs are programmed that way. How old is he, btw? I believe they learn how to "hold" their bladder at about 5 months. Personally, I would just leave him alone in his crate during the train ride. He'll probably just sleep during it
Once you get off the train just keep him in his kennel until you find a safe and secure area where you can bring him out, unleash him, and let him go potty and drink more water. He shouldn't really need to eat anything, provided that you feed him in the morning before you go and later that evening. You could give him some treats that he'd probably love though
Don't worry, everything will work out and you'll do great
Have fun!