Oh the joys of interviewing!! It was actually very fun once you get over being nervous. I interviewed mostly in the South. They paid for hotel,etc and there was usually a nice gift bag when I checked into the hotel.
I agree with oriented. Wear nice casual clothing. Even if the residents are drinking, I personally would stick to soda or water. I would order food along the lines of what everyone else is ordering. The before interview dinner is informal but it is part of the interview process as well. So remember to be on your ps and qs and ask good questions. Hopefully the event will be free of attendings.
On interview day if they take you out to lunch don't order anything with red sauce 😉
If the residents at a particular program have a say in rank lists and are having drinks, I have heard of a couple of places down-ranking a candidate for not drinking (not the type of "not drinking" where the person never touches alcohol, but the type where they seem too scared and uptight to drink). One of the residents at a particular program told me that if someone is not taking them up on their offer to go out and let loose a little, they used that as a gauge as to how well they would fit in that program. I am not saying its okay, just stating a fact at some places.
Now obviously this varies from specialty to specialty, some are less formal than others. For example, I am EM so most of my nights before were sports bar, jeans, button down shirt or sweater, etc.... But my IM friends usually were far more formal with nice restaurants, business casual dress.
If i knew the name of the place we were going, I would look it up on the internet and dress accordingly. If the residents were drinking I would order one, maybe two drinks. At two places in particular the residents were using the night before gathering as their personal gathering time, so they were DRINKING, on the programs bill. I most certainly didn't do that, but don't think that it would have mattered if I did. Afterall, I have an interview the next day...how tacky would it be to smell of alcohol and be sick all day?? Not professional.
To each his own, just go with the flow. Some people feel more comfortable asking questions of strangers after a couple of sips of alcohol. double-edged sword, so be careful. COMMON SENSE WILL PREVAIL!!!