BLESS VINH'S. As other reviewers have said, this is by far the best and most affordable option on campus. The banh mi's are huge and generously stuffed, and won't come out to more than $5.
My go-to are the veggie noodles which are in the fridge near the cash. My only complaint is that the packaging is awkward and messy, but it's so filling and wonderfully spiced. They also have a spice bar so you can adjust the flavor to your liking!
If I'm not in a rush/not broke I like to indulge in the "pho" which isn't particularly authentic, but just such a nice treat on cold winter days. It's only served 11:30-3:30 though :(
The only thing from Vinh's that I didn't enjoy was the steamed veggie bun. I found it to be a bit sweet which was odd to me, but I also don't really like steamed buns in general so that may be it.