There’s no shopping buzz killer like the credit card that won’t swipe. But you can patch that right up by taping a piece of clear tape over the magnetic strip. Sayeth WIRED:
the magnetic stripe on the card are made up of millions of iron-oxide particles that convey information by generating electrical pulses in the reader. With wear, these particles get smeared, creating background noise. Luckily, this noise has very low magnetism, and it can be dampened by increasing the space between the magnetic stripe and the head that reads it. So simply cover the stripe with Scotch tape.