I think that B51 summed things up rather nicely, they'll provide you with lots of coffee, tea, juice, or milk depending on what you fancy. I've also seen omlets, cereal, and other breakfast items. They never have more than 3 choices, but the choices get rotated every few months.
Dinner of course also offers 3 choices, usually a fish or pasta choice, a chicken choice, and a red meat choice. They also offer a light fare, should you not be all that hungry. Again all drinks are free and that includes alcoholic beverages and they have a halfway decent selection.
While the food will be served on a plastic tray, the dishes themselves are glass and you'll have real silverware to eat with, along with a nice cloth napkin. Oh and no TSA's walking by and checking you for knives. :lol:
As B51 mentioned, you would also be entitled to use the Club Acela lounge in Boston. These lounges are a nice quiet refuge in the often-bustling train station. They have nice plush chairs, conference rooms, computer terminals, newspapers, TV's, free soft drinks, juices, coffee, tea and clean safe bathrooms. They also allow you to board your train before the rest of the masses.
In Boston the lounge is actually upstairs above the ticket windows, the door is to the left of the windows and to the right of an information kiosk. There is a small doorbell to the right of the door. Ring the bell and wait for a beep. Just show your tickets to the attendant at the desk and you're in. They will announce when your train is ready.