At one point I did a bunch of research to try and figure out if it was possible to meet the full recommended daily allowance of all 24 essential vitamins and minerals and 9 essential amino acids via diet alone without any supplementation. In theory, on paper, it is possible; but personally, I still take supplements.
My take away was to make the most nutrient dense foods the staples of my diet for the essentials and then to experiment with as many new (whole unprocessed) foods as possible for the greatest possible diversity in micronutrients, polyphenols, probiotics, prebiotics, isothiocyanates, alkaloids, terpenes, flavonoids, etc etc etc which we are only just now beginning to understand the importance of.
Hands down the 3 most nutrient dense foods with the widest array of vitamins and minerals are dark leafy greens, fish, and organ meats. Those three alone will provide almost all the essentials, but not quite. Seaweed, shellfish, nuts, and seeds will help to round out those often overlooked nutrients like iodine, manganese, iron, and selenium. Closely following the big 3 are soybeans, mushrooms, and legumes for the veggie folks, and pasture raised meat, dairy, and eggs for the non-veg folks. While some may not accept it, my research has led me conclude 100% plant based diet requires supplementation of B-12, D3, and DHA to meet RDA levels. Really, for optimal function, everyone should be supplementing these three regardless of their chosen diet. Lastly, of course, we all know you need to eat your fruit and veggies. Throw in a good daily multivitamin and you've got a more or less nutritionally adequate diet.
I think organ meats are gross and i'm not a very big fan of meat and dairy in general, so I don't strictly adhere to eating only what is most nutritious. Fortunately, there are variety of sources for most every nutrient so it's easy enough to adapt to your own preferences so that you can enjoy what you eat and still maintain adequate nutrition.
Here are some random notes from my research:
6 Essential Nutrients
Carbohydrates
Protein
Fat
Vitamins
Minerals
Water
24 Essential Vitamins and Minerals
Copper
Iron
Iodine
Riboflavin (B2)
Magnesium
B12
Potassium
B6
Selenium
C
E
D
Phosphorus
Calcium
Zinc
Salt
Pantothenic Acid (B5)
Niacin (B3)
Molyboenum
Manganese
Choline
Folic Acid
Biotin (B7)
Vitamin A (Retinol)
9 Essential Amino Acids
Lysine
Methionine
Phenylalanine
Theanine
Tryptophan
Valine
Leucine
isoleucine
Histidine
You can get almost all your amino acids in a day from 100 gram servings of:
Pumpkin seeds
Brazil nuts
Almonds
Sunflower seeds
and either soybean, Parmesan cheese, or Fish.
Fish - A, B1, B2, B3, B5, B6, B12, D, E
Dark Leafy Greens - A, B2, B3, B6, B9, C, E, K, Beta-Carotene
Seeds - B1, B2, B3, B5, B6, E
A - Orange Vegetables
D - Fish, Eggs, Cheese
K- Dark Leafy Greens
Calcium - Dark Leafy Greens, Avocado, Banana
Selenium - Brazil Nuts
C - Fruit
Omega 3 Fatty Acids - Albacore Tuna, Mackerel, Lake Trout, Anchovies, Salmon, Herring, Sardines, Tilapia, Whitefish, Sole, Shrimp, Shad, Scallops, Pollock, Oysters, Chub
Copper - Shellfish, Leafy Greens, Grains, Beans, Nuts, Dried Fruits, Cacao
Iron - Chicken liver, Squash & Pumpkin Seeds
Zinc - Oysters, Red Meat, Poultry, Nuts, Crustaceans, Grains, Dairy
Vitamin D - Egg Yolk, Cheese, Tuna, Sardines In Oil, Cod Liver Oil
Vitamin E - Sunflower Seeds, Almonds, Spinach
Vitamin C - Berries, Citrus, Melon - Fruit
Biotin - Eggs, Almonds, Nuts, Legumes, Whole Grains Meat, Milk
Vitamin K - Leafy Greens, Broccoli, cauliflower, Aspargus - Veggies
B-12 - Shellfish, Liver, Crab, Meat, Dairy, Cheese, Eggs
Iodine - Seaweed, Cranberries, Yogurt, Potatoes
Vitamin A - Bell Peppers, Fish Liver, Tropical Fruit, Sweet Potato, Carrot, Greens, Squash, Apricot, Melon
B3 - Yeast, Fish, Poultry, Pork Liver, Peanuts, Beef, Mushrooms, Peas, Sunflower Seeds, Avocado
Molyboenum - Legumes, Beets, Lentils, Peas, Grains
B2 - Liver, Lamb, Milk, Yogurt, Mushrooms, Spinach, Almonds, Tomato
Manganese - Grains, Nuts, Leafy Greens, Tea
Selenium - Brazil Nuts
Top Nutrient Density Foods
Dark Leafy Greens
Fish
Soybean (whole)
Mushrooms
Seaweed
Almond
Cacao
Flax
Quinoa
Pumpkin Seed
Sunflower Seed
Apricot
Avocado
Blueberry
Guava
Papaya
Currant
Garlic
Ginger
Broccoli
Peppers
Carrots
Okra
Beet
Tea
Purple and Orange Sweet Potato
Hope it helps.
P.S. - Don't forget the Mangoes!