This is not revenue to the charity.
You can deduct out of pocket expenses to pay to provide service to a charity. The purpose of the trip must be substantially for the charitable purpose. A vacation where you perform some charity duties will not count.
"The deduction for travel expenses won't be denied simply because you enjoy providing services to the qualified organization. Even if you enjoy the trip, you can take a charitable contribution deduction for your travel expenses if you are on duty in a genuine and substantial sense throughout the trip. However, if you have only nominal duties, or if for significant parts of the trip you don't have any duties, you can't deduct your travel expenses."
Also, the charity must be registered in the US as an exempt organization. Overseas trips won't be deductible even if the organization is a recognized charity, unless the organization has a branch in the US that is properly registered.
