A non-specific piece of roasted beef. Sometimes from the round or the sirloin, but there are a lot of different cuts used. It’s like a very thick steak, roasted or broiled, and sliced thin.
Perhaps the OP started folks wondering - I note that are are plenty of references to Boston Style coffee on Google today. On the first two results pages all references are created after date of OP.
I don’t think that’s so prevalent now, although maybe still in R.I.
But it must be very confusing for someone back then to see “Boston Style” and “Regular” listed as separate items, with different prices.
A few nights ago on Jeopardy, under the “American regionalisms” category, the answer was: A New England expression for what the rest of the country calls a milkshake. I knew the answer was “What is a frappe?”, but I would have been tempted to say “What is a cabinet”. The latter being a Rhode Island-ism and so maybe not qualifying as broadly New England.
I know you are from Rhode Island but the full name of the state is the most descriptive of all states: Rhode Island and Providence Plantations. That about sums it up. You have Providence plus a whole bunch of large islands, the most important being Newport, that are close enough together to be connected by big bridges plus some that are offshore like Block Island. You could do some ocean filling to make it one contiguous land-mass but it wouldn’t do any good. It is still going to the smallest state by far. Some people have ranches bigger than that. Unlike #2 Delaware, though Rhode Island has personality and personality goes a long way. I can be at the Rhode Island border 15 minutes from now if I wanted to and it would be about the same thing crossing from Canada into the regular U.S. culturally speaking. That is one strange little state you have going there and I don’t mean that as a bad thing.