As far as dining halls...where I did my undergrad actually had awesome food/food service, so it's not always impossible to eat healthy at colleges. There was a lot of processed crap and stuff with junk added in preparation, but there was also plenty of good stuff (fresh egg whites were ALWAYS an option at breakfast, there were always hard boiled eggs in the all-you-can-eat halls so I always took a few of those on the way out and stashed them in my fridge upstairs before heading to class, there was always Thanksgiving-style roast turkey and steamed veggies in one cafe Tues/Thurs nights, another place had fresh made-to-order grilled chicken for lunch, made-to-order stir fry, etc...) At least where I was, it became a matter of knowing the various dining locations on campus and what "good" stuff was served when/where. So you may be lucky, too. I also had the foreman grill and always did some cooking in my room. My dorm also had a full kitchen on each floor, and I used that often.
And when you're in a pinch/busy, drinking protein shakes during class once or twice a day is always good. Put some powder in a sippy bottle and when you're ready for it, fill it with cold water from the drinking fountain, shake it up well, and you're good to go.