All the drink at an event like this will certainly be on sale or return[1] so everything he drinks comes direct from the charity's pocket. [1] i.e. the charity

All the drink at an event like this will certainly be on sale or return[1] so everything he drinks comes direct from the charity's pocket. [1] i.e. the charity brings in X bottles of champagne and lets it flow freely all night. At the end they return all unopened bottles, and only pay for what was drunk.