Why do you think they call it "junk food?" Because it's garbage! I think it should only be called junk. Leave off the "food." (Because it isn't.)
Sodas are made of sugar water and chemical flavorings. I like to call them "liquid candy." Many chips are actually ground-up processing remnants (skins, trim, rejected bits) fried in cheap greases. Cheese puffs are also ground-up artificial cheese leftovers, air-blown. Junk cakes are mostly chemicals and sugar. No "junk" "snack" food carries useful nutrition. They are purely for taste. Why not have a snack that tastes good, and helps your body and mind?
Go ahead and snack: Eat something real and really good. Fruit (sweet, fibrous, alive), vegetables (crunchy, almost no calories or fat), or pretzels (only flour, water and a little salt).