If you are a smoker and notice no one is smoking, don't smoke. If you have dietary restrictions, please tell us when the interview is scheduled. Many activities of the on-site interview revolve around social settings where food is served. We will also understand if you have to eat on a fairly regular schedule. DO insist on meeting with students separate from the faculty.
Students are warehouses of information, but never forget the cardinal rule above.
DO remember that you are an anthropologist. Do fieldwork in real time. The onsite interview is an opportunity for you to discover personal enmity between faculty members, learn the unwritten rules of the Department, and discover what Departments really want in a colleague. Van Leunen, MC 1979. A Handbook for Scholars.