There are probably many ways, but disabling every pacemaker and other electronic device within a 100 yard radius may not be appreciated...
Yeah, some jerk would prolly be upset over his pace maker frying, even if you tried to explain to him that it is for the greater good.=o)
Not a problem. Go to Radio Shack (ugh!) and buy a bulk tape eraser. It's just a large electromagnet. Run that over any item of clothing you buy and bye bye any RFID sewn into, or tagged or attached to them.
Since audio cassette tapes have started to become extinct, the bulk erasers may not still be available a lot, but it's not difficult at all to make a simple electomagnet.