Sage is a useful culinary herb which loves our climate and grows with unbounded enthusiasm. My own specimen has been grown in a container for three years with no care or attention other than periodic watering and has reached 3 feet across and seeded itself around, providing a number of nice plants to give away. A major advantage to growing your own is that you can enjoy its lovely Delft-blue flowers, both in your yard and on your plate. The flowers also taste of sage, but the flavor is softer, sweeter, and more floral. They are lovely on salads. Pick them just before you use them, toss them on top of the dressed leaves, and enjoy. This is one of the ephemeral pleasures of the garden, to be enjoyed for a week or two and then let go. But, like most such pleasures, it makes an impression and leaves a memory of a pure and lovely thing enjoyed in its season.
You can buy a sage plant nearly anywhere. I suggest avoiding the variegated or variously-scented ones unless you have space to spare. Common culinary sage is the most useful in the kitchen.