For instance:
Applebee's has a promotion where if you spend $50 in Gift Cards, you'll receive a $10 Bonus Gift Card FREE.
Now, if you are a family of 4. You probably spend about $50 when you eat out in most cases. (4 people with $10-12 entree, plus drinks). If you like Applebee's, then this is the deal for you.
Go to Applebee's. Buy the $50 Gift Card. Use the $50 Gift Card to pay for dinner, and walk out with a bonus $10 Gift Card. Now, chances are the $10 promo Gift Card cannot be used in conjunction with the $50 Gift Card, and it may not be valid for another month or so after you receive it. BUT, you will still have $10 to use if you meet a friend for dinner, or it will be like a B1G1 date with your significant other.
I hope that helps stretch your dollars a little bit further this holiday season! Be sure to pay attention to the restrictions these businesses may place on the deal, and ask before you buy!