Eating chicken after a day or so is very dangerous. The composition of proteins will change, often causing digestive problems. In fact, chicken contains more protein than red meat. It is better to eat chicken cold, but if you feel it is necessary to heat up chicken make sure you do it over a long period of time on a low temperature.
Potatoes are actually very good for you. They contain a lot of nutritional value. However, once you let potatoes sit they can potentially lose their nutritional value, and even become quite toxic for your system.