Assorted magnetic-backed letters, numbers, shapes,and toys
A stainless steel cookie sheet or cake pan with a lid
Bag to keep them in
As you drive along let you child make words or pictures
with the magnetic pieces. Some one call out a letter and the child can find it and put it on the sheet.
Child can call out an object and you can spell it for them as they place it on their sheet.
Another option. Use foam or vinyl sticker shapes on the side windows as they drive.