Many retailers are more than willing to give a donation to your cause. You just need to know where to look. Websites like igive.com and goodsearch.com (which is powered by Yahoo) are free to sign up. From their website, you click on links for stores like Barnes & Noble, Ebay, Gap, Drugstore.com, Fandango.com (there are many more), then a percentage of your purchase price will go to the charity of your choice. Mine is Shwachman-Diamond America in honor of my son with Shwachman-Diamond Syndrome.
For more information on Goodsearch, please see this article.