Yep as said payment to get in etc and the show brochure they sell, also advertising and the money the stalls have to pay out to be there, one reason why food costs more as they need to recoup the charges....
Aircraft also charge for displaying, this can vary from nothing through to full costs or down to free fuel and Oxygen etc ....... you couldn't afford to do it otherwise with the likes of private Spits etc.
RIAT donates to the RAF charitable trusts I believe, but it is not that much when you think of the total costs involved and gate revenues..
When you look at the revenue which is over £5,000,000 and the costs involved in doing it all which is over £4,000,000 and the charity gets some £300,000 out of it, that puts it into perspective.
see the accounts here
http://www.airtattoo.com/Assets/File...&As%202007.pdf