One very cheap item I have found to help me to maintain my nourishment are the 12 ounce cans of V8 vegetable juice. I drank one after every lap of our last 24 hour painfest and it did make a difference on my recovery.
The lap times at the event were around 45 minutes so I'd just say drink one per hour along with your other liquids and some food.
Good luck and have pain...err..fun.