What Should Be a Part of Your Diet?

There are certain type of food that are a lot more beneficial than others, I always ask my self what should be a part of my diet? especially when you are trying to eat healthy or change your eating habits, What is the one food that you would consider healthy and have to include in your diet plan?

Personally I always have those 3 things:

Fish for Omega 3 fatty acids
Oats in my morning whey protein shake to keep me full for longer
Peanut butter for protein, potassium and fats