If you have trouble with portion sizes or can not stop yourself from eating the whole box of cookies, try a small snack size bag. Buying snack size products are ideal to have around the house. When buying a snack size product just grab that one snack size package, eat just that package, and do not go back for more.
Snack size items help you control yourself when eating food, so you do not overeat. When eating something out of a big box or a big bag, it is hard to just quit, you just continue to snack and before you know it the whole box or bag is gone. If you can not buy something that is premeasured in a package, do it yourself. Just measure out a serving size, put it in a bag, and enjoy just that serving size later.