"I have a friend who I want to give two items to: a gift card and a fridge magnet. I want to send them as cheaply as possible, so thought of just putting both in a plain envelope with the Christmas card, sending that first class. But then I thought to myself, would the magnet screw things up along the way? The USPS scanners and sorters, would it demagnetize the gift card along the way? So I ask you: CAN I do this without screwing something up? If yes, alternate ideas?"
Does the gift card have a magnetic strip on it? If it's a scratch-off, then there are no worries. If it's got a magnetic strip, then I wouldn't send it in an envelope with a magnet. My suggestion is to mail them separately. Mail scanners aren't going to hurt a gift card, so wrapping it in foil isn't necessary (and it's also entirely ineffective) but a fridge magnet in close proximity can ruin a mag strip.