Milwaukee Theater is kind of in a strange area..more bars/bar restaurants catering to sporting event attendees. If you had more time I probably wouldn't be recommending these places but they are close and serve pretty good food. If you don't mind walking a couple blocks there are some decent offerings:
Here are some casual stops:
-I love Major Golsby's for their wings (they are different so don't expect traditional buffalo style) and chili. Very casual and very fast and less than a block away from the Theatre. I go there before just about any basketball game I attend. Its no frills sports bar fare.
http://www.foodspot.com/Clients/WI/Milw ... ccid=13509-King and and I, 830 North Old World 3rd Street or Thai Palace, 838 North Old World 3rd Street - Decent Thai.
http://www.kingandirestaurant.com/-AJ Bombers 1241 N Water Street ( good burgers, fun atmosphere, just beat out Soblemans for best Milwaukee Burger on Food Wars)
http://www.ajbombers.com/-Trinity Three Irish Pub has really good pub burgers. I love "The Other Burger", I haven't tried anything else but friends have ordered the Friday Fish fry and like it. 125 East Juneau. They also serve Water Street Brewery beers. Its big so getting a table shouldn't be a problem.
http://trinitythreeirishpubs.com/-Miller Time Pub, 509 West Wisconsin Avenue, Decent enough sandwiches. Good beer cheese soup and fried cheese curds.
http://www.millertimepub.com/- German Beel Hall, 1009 North Old World 3rd Street, Lots of good beer and always a good time. Iif you are running short on time before the show they have pretty good German sausages and other limited menu items including smoked pork chops, beef rouladen, and a fish fry. Almost everything is under 10 bucks and they are pretty fast. Nice place for a taste of Milwaukee.
http://www.oldgermanbeerhall.com/There are some nicer places nearby but I would imagine they would take longer like Capitol Grille,
Milwaukee Chop House, etc.
I have heard good things about The Red Accordian
http://www.theredaccordion.com/food/ but haven't been there.