How can I stay away from junk food?

Okay so almost everyone has the craving of junk foods right? Cookies, doughnuts, cake, cupcakes, icecream, popcorn, ect. Well, I feel like I need to loose some weight over my summer vacation because next year I want to be fit and healthy :) Well, as you know, it's not as easy as we all wish it was/is. I need some help. How can I stay away from junk food? I understand I need it every once in a while but not constantly. How can I stay fit and get fit :) Thanks for coming to answer! All help is appreciated ♥♥♥