I think the fairgrounds has some neat features. The hill towards parking could be used for a gravity race (carlike things on strings) and a paper airplane contest. There used to be a way fancy kit with really stiff paper and you glued the designs together… but, I am not googling it up readily. Could be hybridized with printed bodies and custom paper wings… But lots of room for different categories and crowd pleasing.
The demolition derby! Oh my goodness… large scale robobotics. Or human powered tractor pull!