There's no one food that you could live on forever as the body needs the proper nutrients from a variety of foods to survive.
However for short term survival the one food you could live on short term is potatoes which offer carbs, protein with amino acids and vitamin C to prevent scurvy.
Although potatoes lack the fats and other minerals that the body needs.
You could survive longer on a combination of milk, sweet potatoes, potatoes and beans, which helps improve your nutrient balane.
Potatoes are rich in nutrients and offer carbs for energy, protein, including essential amino acids and vitamin C and potassium.
Eating potatoes prevents scurvy as the vitamin C in potatoes is crucial for long term survival on a limited diet.
A diet known a the potato diet saw a man survive on potatoes and supplements, which showed the potatoes viability.
Although potatoes are low in essential fats and some minerals like zinc and without the other vitamins and minerals you'd eventually become deficient in vitamins and nutrients like vitamins E, B vitamins and calcium without other foods.
Some better combinations of foods to help you survive longer and get more nutrients include.
Beans and potatoes and rice, which is a more complete profile of protein, carbs and fiber.
Potatoes and sweet potatoes, which boost your vitamin A and vitamin E.
And potatoes and milk ,which is a classic Irish dish that adds calcium and fats, although pasteurized milk needs vitamin c.
Some foods that can last forever basically are popcorn, sugar, dried beans, white rice, salt and honey, although these foods don't offer complete nutrient that the body needs to stay healthy, but they are better than no foods at all.