Since interview season is in full swing I thought I would get something up that has some relevance for some of the people I know going through this process. If you've missed Dr. Becca's TT advice aggregator, you may want to check that out as well. There's a lot of good advice there but I though I would tackle the interview dinner today. Typically, this is on the night between your two day interview, often after your formal seminar and with a small group of 4-6 faculty.
The purpose of this dinner is sort of a "get to know you" kinda thing. IME, the conversation is less centered around science and more for the group to get a feel for what you do outside of work and for you to ask questions about the department, the university and the area. People may talk about their families and the schools in the area and you can make a call as to whether or not you discuss your own family/relationship status. The main goal of the faculty is to determine if you would be the type of person they would get along with for potentially the next 20 years and your main goal is to figure out if you are willing to do the same. I have found the dinner to be the least formal aspect of the interview, but no less informative for both the interviewers and interviewee.
Although informal, don't assume that people won't notice a lot about you. As such, here are a few suggestions.
1) It should be obvious, but don't get sloshed. A glass of wine with dinner, sure. Three? probably a bad idea. A bottle or two might be bought for the table, but if people keep offering to fill your glass (and they might) use the "I want to be sharp for tomorrow" excuse and stick with water.
2) If you have dietary preferences or constraints, either make them known ahead of time or check the restaurant menu online to make sure it will be suitable. Better to not make everyone uncomfortable by revealing that you are a vegan while sitting in a steak house.
3) Remember that you are there for the interview, not the meal. Don't take forever deciding what you want to eat or have 34 caveats to your order. You don't need to subtly send the message that you are picky or really difficult. Again, if you are, check the menu ahead of time and decide then what you want. Less time looking over the menu, more time engaging the faculty.
4) Don't pick the most expensive thing on the menu, nor the messiest. A whole lobster is probably a bad idea, on both fronts.
5) Enjoy yourself. The dinner should be fun and an opportunity to get to know people a little. Having some humorous anecdotes and don't let the conversation lag into awkward pauses if you can help it.