If you find healthy produce a little pricey, try gardening as a way to knock yourself up the happiness ladder a few notches and get good grub. It combines healthy eating with exercise (more on that later), along with sunshine and general productivity. All of these ingredients have been proven to increase optimism, zest, energy level and sense of self. You'll get that special satisfaction that goes along with encouraging a fruitful garden, and you'll enjoy the sense of accomplishment that comes when the growing season is over and you're harvesting your bounty.
Of course, if flowering plants are more your thing, that counts, too. All that weeding, raking and pruning can be cathartic and energizing as you free your flowers to enjoy the sun's warmth and the soil's nutrients. Spending time outside can have a serious restorative effect on quality of life and happiness levels. This can be especially true for elderly and developmentally disabled populations, but of course everyone can greatly appreciate the effect.