its amazing how many people on here don't know what causes a hang-over. If you don't know what causes it, you can't easily get rid of it. A hangover is your bodies reaction to being dehydrated. Also, water alone will not always work because the alcohol (depending on if you pissed a lot the night before) can flush your body of electrolytes. Also, alcohol is a toxin to your system, and thus Vitamin B complexes can help. Do not take pain killers to rid yourself of a hangover, the potential side effects are simply not worth it (with the amount of liver and kidney damage that can be caused or damage to the stomach lining). Best bet, go to GNC or similar store (reputable), get a good multi-vitamin (look for B complex vitatmins but be aware vitamin B can be overdosed). Also, see if you can get non-sodium based electrolyte pills. The sodium based pills can have a more greater effect on your blood pressure. If you cannot get these, pick up Pedialyte (gatorade and other sports drinks are too high in sodium, sugar and citric acid) and pound a couple.
Best cure I've found (and I never used to get hung-over but constantly do now, and I have gotten horendous hang-overs from as little as one beer before) is at the end of the night, take 1-2 electrolyte pills and 1 (typically half dose) multi-vitamin with 2-4 glasses of water.
The reason McD's and other fast food helps is because of the sodium content, however, its not exactly quality food and its not advisable to fix a hang-over by bumping your sodium intake.
life is too short to have any regrets