“You’re all set.”
Have you heard this a lot at MIT and in Boston in general? You might hear this from a staff member after dropping off a document, or in the RMV after getting your driver’s license.
“All set” means everything is “OK” or “ready” or “finished.” It originates from the sport of running a race, ie. “Ready, set, go!” In other words, your interaction is finished and you can leave. To exit the interaction, simply say “Thank you.” In response, they might say “Have a nice day” or “Have a good one” (a good day, that is. “Have a good one” is also very common in Massachusetts).
Even American visitors from outside of New England may not immediately understand “All set.” I recall that my parents, who were visiting me from South Carolina, tried to pay for their bus fare, and the driver waved his arms, saying “You’re all set.” They had to ask him, “Does that mean everything’s okay?”