Simple PrePay/Checkout System Using MagCards?

An Anonymous Coward asks: "I help at a small youth club that has various events on different nights. For awhile now we have had a snack bar of sorts and have been thinking of developing a pre-paid system. We have access to plenty of computers and magnetic card readers (wit blank cards) but any ideas on the software? Also, would there be any way of also using this to keep track of a CD sign-out system?"