I feed the same amount and same food as at home. That's because my dog has allergies and a very sensitive stomach and because I make sure he gets lots of exercise at home. I feed a premium high-performance food which is high-calorie, low bulk. It actually doesn't cost any more per calorie than what you get at the supermarket--because it's low-bulk, you don't need to feed as much. You don't need to do as much scooping afterwards, either! Feed your dog only as much as he needs not to get fat (you should easily be able to feel his ribs but not see them, and from the top you should be able to see a definite "waistline"). This amount usually has very little to do with the amount suggested on the package!

Because my dog is prone to vomiting, and I once had to abort a trip because of it, I give him slightly more food per feeding before and after a trip but not during the trip. I also feed him three times a day instead of twice (means an hour's rest at noon) during a trip so he has less in his stomach each time. Your dog, obviously, may vary!

If you're going to change your dog's diet, do it at least a month before your trip, and do it gradually--mix the two foods starting with a tiny amount of the new food and working up to all new food after 8-10 days. Not all dogs have sensitive stomachs like mine, but better safe than sorry!