Rehydration
Alcohol is a diuretic, so part of the reason you have a pounding headache after a night out is that you are dehydrated. Drink plenty of water the moment you wake up in the morning, or better yet, drink coconut juice or a sports drink to replace your depleted electrolytes. It's one of the best ways to recover. For other replenishing fluids, check out this list of shops where you can get healthy drinks and tonics in Hong Kong.