Contrary to what you will sometimes hear some people who are unhealthy are extremely happy, and make the most out of life. However it is far more difficult to stay happy if you find that health restrictions limit what you can do, or on getting somewhere you feel unwell.
Health however does give a feeling of general well-being, and allows you to achieve more, go more places and have greater confidence.
Happy people also fight off health problems better as the immune system functions better, and therefore happier people live longer.
An ability to laugh also helps, as it decreases stress hormones in the blood. Irritable people with no sense of humor, who are impatient, competitive and have extreme sense of urgency tend to be stressed far more and aggressive, which can be particularly noticeable when they are driving. Generally this will make them unhappier, than the laid back person who can see the amusing side when someone makes a driving error.
Exercise that you enjoy and in moderation also makes you feel better, more awake, happier and of course keep fitter. Swimming is said to be the best form of exercise but walking, either in the country or on a tread mill at home comes a close second, as long as a few stretching exercises are also undertaken.
Diet wise, the best is a balanced selection where rather than omitting items if you wish to control your weight you reduce portion size, and add exercise.
