I routinely work with mag stripe cards and barcodes while dealing with libraries and selfcheck out systems. With access to a mag stripe reader I've personally checked what's on various room keys and casino slot cards. In general there isn't much of any value or use that I have ever seen. Slot cards may have a name and your player number recorded but usually nothing more than what's already printed on the card. I've never seen anything personally identifying on any room keys I've checked.