Ahhhh, finally a topic on which I can speak with authority.
Australians already know the cure, it's called "Barocca". Pitty they don't sell it in the USA.
A Hangover is a multi part animal, tackle each part individually.
Dehydration: They say drink water. Well yes, but you also need salts and glucose to make that water into usefull fluids (IV anyone?).
Gaterade is okay, but I don't like it much. What's better is those fizzy rehydration powders available at your local pharmacy. Should be clalled glouca-something. They have salts, gloucose, and fizz (which calms your stomach by neutralizing the extra acid in there).
Toxicity: Dear God man don't drink cheap booz! Drink filtered vodka (skyy or better) and charcole filtered burbon. Your body needs vitamins to catalyse processes of filtering in your liver. Take multivitamins and take a double dose of the B complex.
Your headache: Take some asprin, NOT acedomenafen (sp) or ibuprofen. Both will damage your liver. Also DO NOT take asprin before bed, this is a myth and a stupid idea. Asprin kills one of the enzymes in your stomach that help break down alcohol. Take asprin after you wake up. Alka-seltzer is great because it has asprin, antacid, and salts.
In short take an alka-seltzer (or fizzing gloucose drink) and a b vitamin. As soon as you start to feel better eat a lite meal. This will help your stomach. Alcohol strips the lining real good. Mc'ds is really good hangover food because it has lots of simple carbohydrates (sugar) yet is filling.
Good luck
Godspeed
In the future, to avoid hangovers, eat before you booz. And make sure you're hydrated before you start! A gallon after drink won't help as much as a glass before! Oh and only drink quality booz.