People love a good cause. Your players are no exception. Players will happily get behind a good cause while playing the games they love. This is obviously a great way to build positive relations between your players and yourself.
Why run charity events?
Other than the positive light you and the store will gain, you will also increase sales. Players will happily turn up and spend money, not just on the event, but also on peripherals, such as, deck boxes, card sleeves, fortune cards, food, drinks, etc. Run side events like Draft or Sealed to optimize sales.
What should I run?
You do not necessarily need to collect cash for the charity. A great example of a charity event would be a food drive. Contact a food bank in your area and get an approved donation list. Now have the entry to the tournament be canned goods from that list. Players still buy the packs for the event but the entry is waved for those supplying canned goods for the charity.
You can do something similar for roleplaying and miniature games with the cost for playing/entry being the canned goods.
For more OP ideas contact the Organized Play Department.