Do you routinely snack on things you know are bad for you? What could you have instead?
Look through your cupboards, fridge, and purse or backpack. Pull out the things you'd like to upgrade to a better option.
Make a shopping list based on those better options. Try substituting smaller amounts of more intense flavors for bigger quantities of simpler foods. A wafer thin slice of aged sharp cheddar can be nibbled for more pleasure than a hunk of some orange-dyed bland brick. A 1" square of really good gourmet chocolate can be savored and will linger on the tongue delightfully without lingering on the hips like a Mars Bar, and the darker you go the healthier it gets. Instead of a sugary fruit-flavored drink, how about an actual piece of the fruit and a glass of water?
Now look around for any other shopping items to add to your list. How about some fresh fruit and vegetables? What's in season where you live? Could you cook something good and local tonight? See how you're doing on basic supplies that make it easier to cook at home and pack a lunch.
Check around for any other errands you could do on the way to and from the store – library books to return and grab a movie for this evening while you're there, mm? – then bag the bad snacks to give away and head out to bring the good stuff home.