Many good suggestions already to fill 90 hours in Munich.
Too bad you did not hint on what interest you (sight vs arts). Should you take on the arts theme, museums are sort of spread out. A good couple of hours slow walk from the Residenz to the Alte Pinakothek. The Deutsches Museum is to the east side. A good way to traverse the city is via subway and trams (perhaps get a 1-day pass).
For most if not all visitors to Munich, Marienplatz becomes the natural focus point. Definitely hang out there for a while. Check out a couple of churches, cafes, beer halls (Augustinerbrau is right there) etc. I would go up to the observation deck of the Church of St Peter's where you will enjoy the panarama of Munich. Bring your camera (early morning and late afternoon are best times).
for more specific suggestions, give us some idea of what you are interested in.