I have used Timbuck2's medium messenger bag and Chrome's Citizen (medium) messenger bag. Both bags worked well for hauling a few textbooks and or a change of clothes. Currently the chrome bag hauls lunch box, full change of dress clothes, dress shoes and any works papers I may be schlepping home. The only thing I would caution about is that cross strap messenger bags can become uncomfortable when loaded heavy and worn for an extended commute. Nothing will beat a back pack for long hauls, except maybe panniers.

Best,
Willyk57