I feel that a bit more detail might be needed in such a situation. There were many parties in the early phases of the work, and specificity might help out in providing a full answer to the question. That being said, my initial guess would be that Schindler himself is paying for the party. At the start of the work, Schindler believes that spending lavish amounts of money in order to procure favors from those in the Nazi hierarchy of power is critically important to him becoming wealthy. Some of this involved hosting parties where food, drink, and revelry was evident as guests who attended the party were more likely to give Schindler "preferential treatment," in its most positive sense, as opposed to what the term would come to mean for Jewish individuals and those deemed as enemies of the Nazis at the time.