Hangovers don't just happen like a headache, an ingrown toenail, or cancer. Looking for a cure for a hangover is largely too late. Prevention is the key but there are a few things that can be done to help get through the day after drinking too heavily.
Step 1: Prevention
One of the best things to do before drinking is to eat a hearty meal. If you can't do that gobble down the peanuts, popcorn, or whatever other food is available where you are drinking. Drinking on an empty stomach is unwise.
Downing a quart of water before the first drink will give your body the fluid it needs and help divert the absorption of the alcohol into your system.
Step 2: During
Try to drink only one alcoholic beverage per hour. Sticking with the same drink for the whole night tends to lead to less complications later.
Red wine and other dark liquors usually result in a higher chance for a hangover. The less expensive the alcohol the more toxin and thus the greater chance for a hangover.
Drinking water or juice in between alcohol will keep you hydrated (alcohol is a diuretic and removes more fluid from you than it contributes). The liver needs water to remove toxins from the body (yes, alcohol is a toxin) and the sooner the liver can get to work the better.
Step 3: After
Drink a quart of water, juice, or a sports drink. You've just dehydrated yourself so if you were not planning ahead by drinking water before and during you need to catch up now. A Pedialyte freezer pop is the only commercial product that makes sense to substitute for downing fluids. Most hangover helpers are just providing electrolytes along with the water you drink to provide the same recovery help as a simple glass of juice.
Take a multivitamin instead of aspirin or acetaminophen. You have probably urinated plenty so the vitamins in your system have been flushed.
Many people swear by eating something before going to bed after a night of heavy drinking. A slice of bread is often suggested.
Step 4: Disclaimer
Every person is different and many people have found alternate ways to reduce their symptoms. (I try to only drink Guinness and being Irish, German, English, Scottish, Dutch mutt sure seems to help.) The only certain way to go hangover-free is to not drink.