A great event is BYOB. Posters are put up with only the 4 letters initially. Then the date is added. The buzz is created as people are asking whether they will let us bring our own B. . . ? Gradually the word is released that it's Bring Your Own Banana.
On the appointed day, Student Council provides tubs of vanilla ice cream, toppings, and the bowls. All the students and staff have to do is provide the banana. Put them all together in the proper order and you have a sidesplitting event!
This activity can be of no charge (as long as they BYOB) or you can sell bananas for $1 for those who forget to BTOB's.