Literature on student ideas about circuits largely focuses on misunderstandings and difficulties, with seminal papers framing student thinking as stable, difficult to change, and connected to incorrect ontological categorizations of current as a thing rather than a process. In this paper, we analyzed 417 student responses to a conceptual question about electric circuits using a lens consistent with resources theory. We found that though indicators of substance-based reasoning about current are common in student responses, this reasoning is not predictive of other difficulties reported in the literature, such as "current is consumed" or "the battery is a constant source of current." We also found that students use substance-based reasoning in resourceful ways, suggesting that substance-based reasoning may in fact be a productive starting place for instruction on circuits.