If it is just for a day, donuts can indeed be stored in the pantry or kitchen cupboard. Just keep them in an airtight container. You can also store donuts in a paper bag, but because they can’t be fully closed, they will harden with exposure to air, and they will also be at a higher risk of attracting ants and other insects. If you want your donuts to last for more than a day, then place them in an airtight container and pop them in the fridge. The donuts last much longer and are fresher in the fridge. But be aware, that although they don’t spoil, they do decline in taste and quality.