During a school book fair, we have a staff member on site when the fair is open for shopping (recess, lunchtime, after school) and ask for the school to provide volunteers for set up, take down, and support when the fair is open. At the end of the fair, we donate a percentage of sales back to the school in either cash or store credit (your choice).
We can also do smaller, pop up-style events on campus, such as science fairs and international nights.