I always bring an empty nalgene bottle, then fill it up from the water fountain on the other side of security. Free and drinkable water. Just make sure to put your empty bottle on the outside of your carry on bag when you go through security so they don't have to search your bag to confirm it's empty. As for food, I do the same as when I got to work in the morning. I pack sandwiches, fruit and some chocolate. Only thing to consider is that you have to eat the food before going through customs at the other end. I nearly got in trouble for bringing salami in to the US except I had already eaten it. The sniffer dogs were very eagerly sniffing my bag where the empty lunchbox was.