Before you reach for that snack, ask, "What is it going to do for me?" "Will it give me something good, like protein, calcium, whole grains or vitamins?
If the answer is nothing- try and pick something else. For instance, lowfat or fat free chocolate milk will give you some sugar but also will give you some protein and calcium. Cereal will give you whole grains, fiber. Fruits and vegetables go without saying. Peanut butter will give you protein. Ice cream gives you mostly fat, a tiny but of dairy (is it worth it?) A sugary soft drink or sugary juice will give you NOTHING, except sugar and calories. Cake, nothing.
See where I'm going with this?