For UMass wear slacks and a button shirt. No jacket. Not sure about tie. Might be a good idea to wear one. You can always stuff it in your pocket.

Most night-befores are more chill than UMass.

For the most part, they're really varied (dive bars to catered events in hospital buildings), but I would avoid jeans since some events have attendings present but don't tell you that in advance. Khakis and a polo/sweater will cover you for just about everything.

At UMass last year, however, most people either wore a shirt and tie or shirt and blazer (no tie). It's actually a sit-down catered dinner with 2-3 applicants, 2-3 residents, and 2-3 attendings at each table. It's low key in terms of atmosphere, just a little dressier in terms of looks.