If you are running a book fair in your school you can use these great free scholastic book fair gift certificate templates to create prizes or other incentives to students for the event.
How about producing gift certificates that the parents can purchase for their children to use at the book fair rather than having cash in school.
Using a book fair gift certificate will also provide a way to promote particular book titles that the school feels would be of educational benefit to your students. Why not create a discount gift certificate or voucher against particular titles.
As they are fully editable and printable from your desktop you could personalise them to individuals as prizes and make a show of it on awards day prior to the book fair.