according to world english dictionary shaft is a slang term meaning "to have sexual intercourse with" and Sack as in a Ballsack a.k.a Your Testicles inside your Scrotum, so Shaft My Sack Means "To Be Intimate/Sexual With Ones Testicles"
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".