If you get so much in pledges, go in a drawing to make a principle sundae-- since you can't really have too many students putting chocolate sauce, strawberry sauce, whipped cream and such-- than you could have a drawing and pick XX amount of students afterward-- incentive to get pledges...

We did the stove top hats from US TOY Carnival/Novelty Division website and they had our school colors. They were a few dollars each and the kids had a blast with them. They could also wear them to the spirit days at the school.

If you get donated items, you can have a tier program of prizes. The more laps or longer amount of time each person jogs, they qualify for a specific level of prizes.
Have inspirational messages around your course & plenty of water on hand - small bottles since some only take small sips when jogging.
Have all results posted in a central area at your school, posted in your newletter or school website. (recognition is great)
Ask your local newspaper or TV station to come and cover the event (kids love attention)
Ask you Principal if they could offer something like free admission to a football game or something for those that participate. It shows the school supports your efforts and may increase participation.
Have parents bake treats for after the jog a thon since you will have lots of hungry students.

I too am putting on a Jog-a-thon this year and looking for new ideas for prizes, etc. Have any suggestions.

I am a student at a brand new school and i am starting new traditions. This is the second year of my high school. I will be putting on a jog-a-thon and need some ideas. I want to make it fun for every one. All ideas would be appreiciated.