An Iron shirt is a shirt made of iron, there was a superstition that iron could drive away evil spirits, people used to carry iron in their pockets. In the reggae song "Chase the devil" by Max Romeo he sings about this.
Someone who is addicted to obtaining money and building wealth. A money addict and fanatic. Breadheads often work more than one full-time job, and some even participate in illicit activities to "obtain the bread".