It's not as if he's depriving the charities of money because he would have paid the large admission fees if he wasn't doing this; he just wouldn't go. And his presence there is not causing the charity to spend any more money by hiring more staff. There is the real cost of the food and drink he consumes, but depending on how the event is catered, if there is food left over, then he's not effecting anything, and if there isn't food left over, he's taking money out of the other attendees' pockets, not the charity's.
In fact, maybe he contributed to an enjoyable experience for the other attendees, which will make them more likely to support that charity in the future.
Utilitarianism FTW!