How does one achieve 'Happy'?

I worked at a camp this past summer with teens with moderate to severe disabilities, both mental and physical. I often found myself thinking about how little it takes to make these teens happy. I could walk into the camp room, make eye contact with and just say, "Hi, Em! How was your night last night?" and she would be smiling away. Happy as can be, just because somebody gave her a minute of their time and said hi. This camp made so many kids so happy because of the mere fact that we showed up and played with and talked to them. 

I think our society takes for granted happiness, and how its achieved. I believe we tend to brush off quick social interactions or nice gestures as part of everyday life. This camp made me realize that we need a few more people in this world that appreciate the small stuff. How do you think happiness is achieved?