So maybe I'm just overthinking this! I have never been the recipient of this, and I rarely go to DD/Starbucks/fast food so I rarely think about doing this.

But how does it actually work? Is it cash only? But then could the cashier just pocket it for themselves? I can see credit working for drive-thru since the cashier usually knows the total of the next order already... But what if you're physically in line? You'd either be covering the next person's order fully, partially or even have some left for the next next person?

I want to do this but clearly I live under a rock!