If you do everything "right"-- no grains or bad oils, no processed food, consume a healthy ratio of carbs/protein/fats to suit your lifestyle, get moderate exercise, decent sleep, lots of sunlight, minimal stress, at an appropriate weight for your size, no health problems (as in, no formal diagnosis of anything), and generally feel well, happy, good energy... do you need to supplement with anything? What supplements do you take, and how did you decide to do so?

(Not that I think my diet and lifestyle is perfect, but just wondering how I can spot deficiencies and supplement as needed..)