I didn't know I was having a csection and ate normally that day, had breakfast about 6hrs beforehand. When my dr told me I needed a csection he said the worst that could happen was that I vomited which could effect my breathing. I didn't have any problems tho. However, in saying this I would eat or drink anything further as I'm sure you could do without the risk!
It was hard for me also I was beyond dehydrated at night and it seemed worse knowing I wasn't suppose to drink anything but I wouldn't suggest drinking anything
The main reason to be NPO is t prevent you from aspirating. I would recommend ice chips if you are really desperate. Don't go guzzling a gallon of water.