Haha well dorm life was actually how I gained about 70 of the pounds I'm carrying now because of how awful the dining halls are. I now live in an apartment and no longer have a meal plan where eating healthier is much easier.
As far as the dining hall goes - I would suggest salads (I don't like salads though so that was a problem for me) or sandwiches (my dining hall always had a deli bar open). I also had the experience that they usually had vegetables and select fruit (i.e. green bananas and red apples, sometimes oranges) but that's about it for the dining hall. In your dorm - quakes rice snacks, wheat crackers and laughing cow cheese wedges, sandwiches of course, fruit, almonds, granola bars (but only have one - most have like 100 calories and 10g of sugar or whatever), 100 calorie packs (again, only have one - they often have a few grams of fat and lots of sugar), soup, beans, etc.
The last two were if you want a hot meal. Soup is a good option depending on what you get. I like regular chicken noodle but I get the 25% less sodium version but even better if you like vegetable. Cheese is out, obviously.
And beans are a superfood as long as you're not getting sugary baked ones or whatever. Many vegetables come frozen or canned so you can heat them up in a microwave. Also, does your building have a kitchen? If so, utilize it when you can to make a healthy meal and then save the leftovers to heat up in your room.