You can get a free order of medium fries at McDonald's today with any purchase that's at least $1. But first you have to download the McDonald's app . . . order through it . . . and then pay for your order using Apple Pay.
This isn't actually a 420 promo. They're doing it next Friday too. And it looks like they've been running the same promotion EVERY Friday this month, but just didn't promote it enough. So no one knew about it until now.