By my definition, caloricly free (or um on sale) is a food that takes work to get, so you burn all the calories (or at least some) in the process of getting it.
My favorite way to do this is to walk to subway on my lunch hour.
A 6 inch veggie sub, with no cheese and only mustard as a condiment (Since mayo= yuck anyway) is 230 calories.
I have to walk about 13 minutes to get to Subway, so I round down to 25 minutes for calories. 168
That burns 168 calories, so my lunch only "costs" 62 calories.
That isn't bad! Throw in a diet coke, and some sunshine and it is a pretty good lunch!
Another great way to get a calorie "discount" is to go on a picnic over the weekend. For me, the weekend is a dangerous time, because I have less of a schedule, and boredom eating is a huge pitfall. So packing a picnic lunch and hiking it to a nice spot to eat is a great way to lower that calorie count.
Especially if you have a craving you just HAVE to satiate, walk or run or bike to wherever you have to go to satisfy that craving!