Potatoes and all other root crops.  

These are excellent sources of starch and almost all the food elements we need.  So eating them in abundance and frequently is an excellent practice.  I always try to cook a surplus and keep the left overs in the fridge for either snacking or reuse in another dish, such as forming part of a bread recipe/pizza dough, for melding with other fillings, a cooling agent for risottos etc or a thickener for soups.