Anything that tastes good! - Just kidding!
Well, since I don't own a microwave, that cuts out a lot of what I consider to be junk food. Actually, I tend to stay away from the entire frozen food section at the grocery store.
Since I'm a calorie counter, just about anything that is high in calories has become "junk food" to me. Of course, there are high calorie foods that are also high in protein and nutrients and all that other good stuff, but I usually can find a lower calorie alternative as a substitute.
At first, I was a little surprised when someone mentioned those 100 calorie packs, but I do have to agree that they are junk food. As someone who grew up on bags of doritos and cookies, those 100 cal packs are a way for me to indulge (in junk food) without really indulging. There have been so many times when I've picked up a bag of doritos, sorely tempted, but then I turn over the bag listening to the gentle rustle of the flavored chips within only to find that I can eat a full nourishing meal for the same number of calories in that bag. So I sadly set the bag back down.
I still eat those 100 cal packs, but not every day. I treat them as junk food should be treated - as a once in a while treat. Maybe some day, I'll get a bag of doritos...but not anytime soon.