Charity Vouchers

I work for a leisure complex which includes a restaurant (limited company).  We often give (FOC) vouchers to charities to offer as prizes for recipients to come and enjoy a meal with us at our expense.  These are logged when they are despatched but an accounting entry is only logged when they are redeemed.  At the point of sale the transaction is "comped" meaning it is not logged as business income and no output VAT is accounted for.  I need to show these charity vouchers in our P&L and put through a journal for management accounting purposes.  What should this be simply cr Sales full retail value and dr Charity Donation full retail value.  Ignoring any VAT?  Obviously the cost of products (i.e. food) is already in the p & l but is a raw goods largely zero rated.  However if the meal includes wine there is a VAT element.  Working out the cost price of each element on each voucher redeemed though would be a nightmare.  We are a large business and do a lot of these vouchers!  Any help appreciated.