Step 9: Put on a play/skit!
Let the kids plan and put on a play at the rest stop. Not only will it burn off energy, but it will be constructive play in a limited amount of time.
Between rest stops have them plan out a play and put it on for the adults, at the next rest stop. They can write lines, they can plan costumes, etc.
Next, after everyone has gone to the bathroom, find a nice picnic table and watch the play!