All of these will calm your system down, so try to eat some every day.
Berries: all types – blueberries, strawberries, raspberries, etc.
Green Vegetables : the darker the better – spinach is better than iceberg lettuce, for instance.
Turkey : this helps you sleep, so have it with dinner rather than lunch, if possible.
Sweet Potatoes : contain more antioxidants than regular potatoes.
Avocados : they help lower your blood pressure.
Nuts : packed with B vitamins, which help lower stress levels.
Oily Fish : omega fatty acids control cortisol levels, plus they boost concentration, which takes a battering from too much stress