Yes, you can buy happiness.
You just need to know what to buy: People.
Ok, not exactly. According to this book 'The Geography of Bliss', by Eric Weiner (that's 'e' before 'i', ok) because human is a party, eh, social animal (rawr), happiness is about being with other people. So, one way to be happy is to spend your money on other people. Be it to buy something for a stranger, friends, or family, when your money help to make other people happy, you'll be happier too.