I'm not a college student, but I was only a few years ago. I understand the culture of "different rooms" and the unplanned nature of many college days.
That being said, Michael's advice is just about right - willpower. It's one thing to "know" and another to "do" -- and saying "it's just too hard" is more than likely an excuse. I'm not saying that to be mean, but sometimes we all need a bit of a wake-up call.
Some easy things you can do:
1) If you know you're going to a friend's room, eat a snack beforehand so you are less likely to be hungry and tempted.
2) Carry a bottle of water with you and drink it instead of snacking if you're really not hungry.
3) At the dining hall, eat alone if what's on your friends' plates is tempting you (or if they're teasing you for getting the broccoli instead of the fries). Or, load up your plate before you get to the bad stuff. I remember at my dining hall that the "short order" fried stuff was always at the end of the line. Easier to avoid if your plate already has other more healthy-for-you things on it.
4) While you're at it, don't go to the McD's or whatever fast-food is on or right next to your campus (on mine it was a BK just around the corner).
5) Walk to class if at all possible. I walked everywhere on campus. Easy 15 lbs. lost with no effort at all.
6) Don't make excuses. Stop. Right now!
Female, 31 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 10/22/14 = 175.0 (net: -40.2)
Last mini-goal: 175 lbs. REACHED 10/22/14 --REWARD: New wallet
Current min-goal: 170 lbs.
Next large goal: 165 lbs. by 12/25/2014
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130-140 lbs.
"You don't have to change your life today. You only need to change your day today."