Here's what I did today:
Bought 4 packs of Trident (assorted flavors, on sale for BOGO Free)
Used 2 Buy 1 Get 1 Free coupons from the 3/6 Smart Source
I would recommend buying a couple of other things to minimize the chance of the cashier getting weird on you. If they scan 4 things and the total is zero, they usually think you are breaking the rules...
There is also a $3/3 American Greetings cards coupon in the ad this week. If your store has a $0.99 section, get 3 for free! This worked perfectly for me with no beeps!