Actually, refuse to go down the snack aisle. I like some junk food, too, but they are a drain on the pocketbook with very little nutritional value. You can try making snacks, some wholesome ones are peanut butter and crackers and carrot sticks with dip or salad dressing. They cost too much and the sugar and sodium content in some of these cereals is frightening. Flour, Brown Sugar, Milk, and Eggs - Vary the amounts and with a few other ingredients with these you can make a variety of wholesome foods for your family with very little money.
Some examples are pancakes, muffins, biscuits, and cakes.
What also helps is to sit down once or twice a month and plan your meals, weekly if neccessary until you get the hang of it. If you have time and the space, pre-cook your dinners and then freeze them for the week. Just as good and much cheaper than pre-made frozen dinners. It's also very helpful to go to discount food stores. If you have an open air market in your area check it out, you can buy bags and bags of fruit for what you would spend at a regular grocery store for a few bags of apples.