Hello, Pick up weight lifting. If you are one of those people that can eat as much as you like without gaining and are young, don't worry about it. You will fill out when your body is ready.
Gee wiz, now you've got me thinking about when I was young. Man did I love corned beef and cabbage with mashed potatoes and lots of butter! I alway ate 2-3 plate fulls of the stuff and never gained any weight. My mom even made me wonderful milk shakes every night, sometimes she'd put a banana in them. I even ate half of a regular pizza with the guys. (We used to see who could eat the most...Oh, I am a female....I just enjoyed the competition.) Now I can't eat the same amount with out putting on weight and raising my cholesterol, so enjoy the food while you can. I will admit that I never did eat many potato chips; eventhough, I loved them. I would only ever eat 6 chips at a sitting.