The ingredients list and the ingredients list only. The ingredients list can tell you what food is in the product. This can help with allergies. Sometimes some foods can even have acids and or metals. Its weird knowing that some foods have titanium dioxide. The ingredients list can also tell you about nutrition. Whether or not that product can give you a balanced meal. For example, if this Kraft mac and cheese has any source of protein or vegetables ect.
Hope this helped!
Have a nice day.