I spent about 30 years in Mass., so I have a pretty good idea of what works.
Turtlenecks and sweaters are good; they're more forgiving about sizes, and if you're not used to the cold, it's nice to have your neck wrapped up. (Also, to keep your neck warm, get a wool scarf if you can.) The only problem with the turtleneck/sweater combination is that you should be binding pretty effectively, since both will drape around your chest.
Long underwear is good; you can get by with just the lowers unless you're going to be outside a lot. Don't get the heavy "waffleweave" cotton stuff -- it's hard enough to get men's pants that don't emphasize our hips, without adding a thick, bulky layer underneath. Get silk or poly -- your best bet for these is to order online from Campmor and/or Sierra Trading Post. In fact, you may find these are good sources for other clothing as well -- they specialize in closeouts and such, and they have good sales.
Where in Mass. are you going to be, and how formal are the people you'll be with? Unless you're in Boston and going out quite a bit, the chances are you'll be OK with fairly casual clothes; but even there, you can probably get away with a dressy sweater rather than a coat and tie, if a decent jacket isn't in your budget. It wouldn't hurt to ask whoever you're staying with what the norms are, especially for Christmas itself.
A good pair of walking shoes or boots is important, especially if you're going to be outside much. Get Goretex if you can -- New England can run to slush. They don't have to be super-insulated, but you want something that will keep your feet dry. STP has good prices on footwear.
Last but not least, when you're shopping for all this, try to get stuff that all goes together, so you can mix and match and get by with fewer items -- you'll save money and have an easier time with baggage.
Oh, and... gloves. And a hat.
And yeah, if you can afford L.L. Bean, more or less anything you buy will be correct for New England.
