Well, we will need to invent some new things to do with no or little setup. While you could draw some tulips for a trek from the car show to a certain watering hole, anything beyond that would require you to do some research. Most people don't want to do any research, or mapping, boards, etc.
For a scavenger hunt, all you'd need to do is to pass out some blank pages and then call out the items to find. Hide & seek only requires you to set certain limits (how far you can go from HQ, how long before the 'seek' begins, etc.)
For the marble or candy toss (candy is biodegradeable in case you miss) is simple, except that IMO, you need a second person to toss or catch the catch the item. You don't want the driver to be distracted from safe driving, and getting hit in the face (with candy even) can have potentially serious consequenses.
Is it more clear now?
Usually defining the problem is the hardest part of doing anything.
Another idea:
drive a certain distance down the street (like 5 lights) catching all the greens with or without using the brakes.