What I was surprised to learn is that you can actually add the tip to the gift card itself, even though they don't receive it until after you and the gift card leave. I had several servers tell me this, so finally I tried it-I added a tip amount after the gift card had been returned to me. The next time I used the gift card, I checked the balance and sure enough, the tip amount had been deducted, exactly what I posted on the receipt. I tried it several times after that and it always worked perfectly. No cash necessary. Now if could just figure out this "Apple pay" stuff.