How about having the cars go to different locations(giving that location some free publicity in exchange for a donation) and do some small task using some stuff(donated by that store/restaurant) to make something(easily assembled) to be donated to a charity like book shelves,tables,chairs,kids playground all done on a time limit for a prize...in other words sort of like a beat the clock deal/scavenger hunt..who ever makes it to all the different stops and builds their piece of furniture/decorates a cake,cooks a pizza/hot dogs/hamburgers(at the different restaurants in the area)and shops for stuff at a store(for the needy/charity) and makes it to the last stop first wins..
