If you must have a particular food, buy a small amount, and certainly not the big bargain size. Instead of buying a big brick of ice-cream, you can buy a small cup of it. If you have craving for fries, choose the smallest packet and take a few from it. give the rest to someone nearby.
If you have weakness for sweets, satisfy your sweet tooth. Choose a sweet like a candy or peppermint which has only 25 calories, last for quite some while in your mouth, and tastes heavenly. If it is a high calories sweet, take just a bite. A taste is what you want, and not the calories.