IMHO there's a good variety of dog tastes in New England. What I think of as a "traditional" NE dog will have some pork in it, like the old Jordans (which are kind of trashy mild little suckers, but kids love 'em and they go well with ketchup
), Roosy's favorite Maple Leafs, and the very porky R.I. Saugy. Tastes have been changing, however, and most of the dog shops I visit are doing all beef, I'm sure in part to draw customers who do not eat pork.
Personally, I think the key condiment to a N.E. dog (if it's not a NY System or other chili dog) is relish. Gotta have a good piccalilli or pepper or tomato relish to distinguish your product. I'm a big fan of baked beans, as well, but that seems to fly only in certain areas, and they're not worth doing if you don't do them right. The Spike's chains I've visited are doing pretty good beans these days, although they do nuke 'em for serving.
As for rolls, a New England style is best, but you have to be able to grill them, and they're not for oversized dogs. If you go for the quarter-pound "gourmet" dog with lots of toppings a fresh roll with a bit of crust works well.