Bring along some paper and pens or pencils. Use your time to make up a story. You can use your names as the characters' or make up new ones.
Use menu items to come up with place names, or secondary character names.
Come up with a beginning, middle and end to your story with your children. Have them decide what happens in between. If you have a budding artist in the family, have them illustrate your story.
You can even do this without a pen and paper, just use your imagination and tell the story. Have each person say one line of the story and see where it takes you!