Happiness is a state of considerable pleasure and cheer. The happy person is often gleeful, light, and even euphoric. Happiness is wonderful. The mind and body may be overcome with elation. It is a beautiful "place to be!" However, happiness may come and go. Contentment, on the other hand, is often a way of life.
An example may be the parent who watches his or her child graduate from college. They are proud of their offspring and happy to see him or her reach one of life's great goals. Yet...even during the ceremony, the parent's thoughts may drift to school loan payments (and how they'll deal with them), whether or not their child will be able to find a satisfying profession, and, perhaps, a sadness of knowing that their child will soon be leaving home. They might find themselves being discontented while, at the same time, experiencing happiness.
Contentment is different. It is a feeling of peace with one's self and one's life, an ease of mind and satisfaction with one's state of being. Happiness adds a certain texture to the contented person...a taste of extra satisfaction to an already satisfied state. Yet - there is also a constant calmness to the contented person's "soul."
Happiness might manifest itself when one buys something "new," enabling the buyer to sense fulfillment and joy. The contented person may realize that they are fine with what they have and that just "being" and feeling nature's energy is fulfilling enough.
Experiencing happiness without contentment may leave a person "empty." But, meshing happiness with contentment can lead to a life filled with calmness, love, laughter, and relaxation...no matter how many things and how much money a person may, or may not, have.