The Ivy is just around the corner - OK (not great) Italian-centric small plates, with a really reasonable and nice wine list. Atmosphere is cozy.
Bina Osteria two doors down from the Opera House is supposed to be good (I haven't been) but is very pricey.
Are you going with kids? I took my 8 year old daughter on Sunday afternoon. We opted for Sel de la Terre in the Pru and then took a quick cab over to the Opera House. But her second choice was Gourmet Dumpling House, which would have been much closer.
Have fun! The performance was beautiful.
Italian in a nice room..Bina..Wahington St
pub food..Max and Dylans..West St
hi priced but good Indian buffet in a nice room..Mantra on Temple
great Thai..Montien on Stuart....be sure to ask for Thai menu..also good sushi
Chinatown is great but you could start a thread on it alone.
Lots of options that are nearby.