Breaking glass in A LITTLE NIGHT MUSIC

In the current bway production the top half of the glass breaks off from the bottom half. It works fine that way. Or you could even have a glass shatter on a picnic blanket in that scene, which could easily be picked up in the blanket.

You can find any number of online retailers who deal in breakaway prop items.

Hopefully though in the way the rest of the show is staged there is either an adequate time to sweep the glass up, or it is being broken into an area of the stage that is not being used again. Even breakaway glass shatters into some very hard and sometimes pointy pieces. A lot of characters are getting ready to run and roll all around that stage shortly and the remains of a champagne glass are not something you are going to want underfoot at that point.