Stuffing 50 lbs. into a 1'x1'x2' space will require some pretty heavy items. If, as a student, you're lugging a lot of books and papers you can probably do it. If it's not all heavy items, though, you might want to consider the large size. It's still within airline size limits.

The Eagle Creek bag referenced above looks interesting but the frameless design would require very careful packing. LLBean's reputation would assure you theat you would have a strong, reliable bag, but I've personally never owned one. The color choices will let you select an option that you can easily find on the carousel.

JimS