If you have an early flight out of MUC, consider the park and fly offer: http://www.kempinski.com/en/munichai...tPackages.aspx

Otherwise get a cheap hotel in town, buy an airport city ticket for 10.80€ and take the S8 or S1 into town. Get out at Marienplatz, take a look at downtown, then the BMW world to check out all the current BMW models and a paid tour of the plant (optional) if the weather is bad. If the weather is fine, stroll across the olympic park just a cross the street from the olympic park. For afternoon/dinner do the kitschy Hofbäuhaus or walk thru the Tal to explore the night life.