I've just read this article in Asterisk about Oral Rehydration Solution - a simple way to treat dehydration during sickness that has saved millions of lives around the world. My speculation: also the most effective way to rehydrate a hangover too?
Either way the homemade ORS of 6 teaspoons of sugar and 1/2 teaspoon of salt dissolved in 1L of water is definitely going in my home remedies list.