How to gauge how professional/formal to dress for a tenure track interview Departments vary a lot by discipline when it comes to what is acceptable attire for men and women both on a day to day basis and at interviews.  Some demand a suit, while this would be ostentatious at others.  Whereas some wouldn't bat an eye at seeing a backpack at an interview, while others would sneer at anything that isn't a leather satchel.  For instance, I've been eyeing this convertible messenger/backpack like this for a job interview (in environmental sciences), but my colleague in the MedSci department says leather or nothing.  Are there any rules of thumb to determine what is and is not appropriate when interviewing at an institution whose office culture you're not familiar with?
I have been on the hiring side of several dozen academic job interviews.  As such, I am somewhere between amused and alarmed that you think your bag will figure into the job selection process.  If your research concerns the bag or if you were giving your talk from inside the bag maybe -- otherwise, how does this even come up?

Preparing for job interviews is a good thing, but I advise you to concentrate your preparations on the things that could matter.  Perhaps you can further work on your slides or on some other aspect of your job talk.  Perhaps you could do further research into the faculty of the department and plan specific things to say to each of them.  And so forth.  These sorts of preparations are still unlikely to make a difference in the outcome...but more so than ruminating on your choice of bag.

Good luck.