What is "dinner money" in the play, The Flick?

“Dinner money” is the name given to a complex scheme of pocketing used tickets and reselling them. Past and current staff sof the theate have put the embezzlement in place to get themselves a little extra income. Secret and illegal, the scheme has been in place for years; however, it ceases at the end of the play when Paul, the new owner, catches on to the deceitfulness.