What you eat doesn't need to be junk. But it will need to be calorically dense (given your small appetite) and flavorful. Try to limit your fiber intake and pick foods that are both healthy and that you enjoy. You can still avoid overly processed crap and all the additives that usually go with it.
Making healthy food choices can be considered as a separate goal, regardless of what your bodybuilding goals may be at the time.
Mainly, what I am getting at is...you already have a license to eat as much as you want while not getting fat. Taking advantage of that is obviously fun. If I were in your shoes, I sure would use it from time to time. But creating a state of optimal health can go hand in hand with bodybuilding also. Making junkfood choices frequently won't really work toward that end.