Good displays go a long way . See restaurant supply stores or any gourmet kitchen supply shops. The jars are relatively inexpensive and they perform double duty as flour and sugar canisters in the off season. Large cookies, even if they are priced a little higher, go first. Don't forget the teachers .
Bake sales appeal to all ages.
Now that I know this, I try and make a few quick breads such as a butter pound cake, banana loaf, or marble Bundt coffeecake for the adult customers who are very appreciative. Also, adult clients prefer things nicely wrapped or somewhat hygienic in appearance. Bakeries will sell you a few sheets of bakery boxes that work well to present baked goods. Consider a Bake Sale Cookbook as a fundraiser . Plan to be there - regardless of what you contribute.