Southborough MA Weekday Breakfast
there is a small cafe/diner in the middle of Southborough called Mauro's that has decent breakfast food. It's right on Main St/Route 30 slightly east of route 85.
Another option, if it doesn't have to actually be IN Southborough would be Harry's Diner in Westborough on route 9.
If coffee and pastries is all you are after, there is a Starbucks, and also Red Barn Coffee roasters, both on route 9 in Southborough.