Bananas. Bananas are a well known source of potassium. However, they don’t have quite as much as some other foods, but still provide around 400 mg of potassium for a medium size banana. Bananas also have other nutrients like fiber and vitamins C and B6. Bananas are an excellent healthy high energy snack. They also form the base of many healthy smoothies, making it easy to get the nutrients in tasty ways.