Another employee tells you that he has been taking home a few supplies because he feels his pay is too low. what would you do?

As a manager of the company, I see this incident as a manifestation of an employee's poor values and work ethics. Firstly, the employee would not be working if there wasn't a job offer. The salary is specifically stated in the contract. So, by signing to the contract, the employee accepts the offer and must live with his decision. Second, it is definitely unprofessional to steal supplies just because of the low compensation. He should address his concerns to his supervisor, or to me as a manager. Maybe we would have reached a compromise depending on the performance. Nevertheless, the employee should be fired from his job.