The best portions for meal prep depend on your individual dietary needs and goals, but a general guideline is to fill half your plate with vegetables, a quarter with lean protein, and the remaining quarter with complex carbohydrates. For example, a balanced meal might include 1 cup of vegetables, 3-4 ounces of protein, and ½ cup of cooked grains or starchy vegetables. Adjusting these portions based on your activity level and nutritional requirements is key.