I would give him a soda crackers or some bread - this helps get him energy immediately and will help absorb nauseous juices. If he keeps that down, give a bit more - wait a bit, then feed him his food later so he doesn't get a really empty tummy overnight. Also, dogs can be given Pepto - so you could also give 1/2 tsp of that now or with the food. You could also give it next time you travel.
Childrens liquid benadryl and/or ginger is also good for travel.