What is the ruling on eating foods whose contents are unknown, or eating the food of non-Muslims out of necessity and unavailability of halal food, especially in a country where the majority of its inhabitants are not People of the Book?

It is not permissible to eat from the slaughtered animals of those who are not People of the Book. However, it is permissible to eat other foods from them, apart from slaughtered animals, unless it is known or highly probable that the food contains something forbidden. One must avoid their food that contains forbidden elements, such as pork or their unlawfully slaughtered animals. But there is no harm in eating what is free from these. It is not permissible to eat from their forbidden food except in cases of extreme necessity where no alternative is available.