Taco Bell is having a deal right now where if you buy a $20.00 gift card you get a free Chicken Flat Bread Sandwich, 2 hard tacos and a drink.
Here is how I have been successfully getting the free meal deal for free multiple times
1. Do the deal pay $20.00 get the free food and a $20.00 gift card. Yout cost $20.00
2. Order the same deal , pay $20.00 with the previous $20.00 gift card = zero out of pocket and now you have a new $20.00 gift card.
3. Rinse and repeat paying nothing each time you roll it.
You can roll this deal over and over for free
**This is a total YMMV (your mileage may vary)
There is no guarantee your store will allow you to by a gift card deal with a gift card but (knock on wood) so far it has worked very well for me.