There are a variety of answers to this question.
From a national agenda angle, at least in recent years typically perpetual resources might refer to renewable natural resources, the theoretically plentiful water supply, or maybe even the capacity to mine minerals in outer space.
In my own writings I have defined it somewhat differently.In my alternate view, there are at least two other views: (1) it could refer to a library of immortal writings, such as those that could be constructed using [souls of literature, in other words, as opposed to human souls]. (2) It may refer to a perpetual motion machine, perhaps even one that has been proven to work. More on that HERE: