It really depends what kind of things you are donating to charity...
When a charity asks us for a "straight up" donation, we give them a gift certificate ( or a few ) and then track their redemption rate.
If we are helping them fund raise with an in-restaurant event ( "spirit night" ) then we look at average sales for that day part compared to what we did with the group in the property.
If we are donating product then we often ask for the ability to have a representative there at the event to hand out coupons - or at least leave them available for people to pick up.
In ANY case we always try to get "up sell" it and get more involved. Can we donate coupons for people to pick up at the event? Can we have our mascot come out to the event to interact with the kids ( makes it more exciting for them and more of a fun atmosphere ). Can we have them on property for a fund raiser.
We then track whatever coupons we hand out for redemption rates as well.
Its really quite difficult to track the tertiary benefits from these activities tho - how much business do we get because of the goodwill our actions generate? How many customers now know about the restaurant whereas before they did not?
There have been case studies comparing non-charitable ( or LSM for that matter ) restaurants and those who do interact with charities and the community and guess who almost always comes out on top ( ESPECIALLY in the long run? ). You guessed it - those who interact. Now, the nay-sayers will say that it could be because of a host of things ( and frankly, I tend to agree to a certain extent ). Operations, customer service, food quality, price, etc -- these are all factors as well.
But in my experience ( whatever that is worth ) --- it works. But remember -- it is often a long term investment unless you are hosting on-site events.
We talk about some of these concepts here:
http://www.restaurantdoctors.com/201...ing-ideas.html
and here:
http://www.restaurantdoctors.com/201...nig-ideas.html
As well as part of an ongoing series.
Feel free to PM me if you'd like to discuss it more. I'd be interested to know what you are working towards....