I spy... Together, make a list of ten things you hope to see on your trip, such as a traffic light, a dog, and a taxi. Then try to be the first one to spot them.
Scribble art Give all passengers a washable marker, paper, and a hard surface to write on (use a book or lap tray). Have everyone draw one squiggly line on the paper, then trade with someone else. Now try to make a picture out of what's there. Can each of you guess what the other's drawing shows?
Post it Take along Colorforms and stick them to windows and lap desks. If you use the set of classic shapes, give your child specific challenges: Can she make them into a car? A horse? A house?
Handmates Take finger puppets or, with a marker, draw funny faces on your child's fingertips. Then let him put on a puppet show for you or his seatmates (a good way to keep a younger sibling entertained).
Homemade puzzles On your child's tray, break a large cracker into several pieces and see whether she can put it back together. She can make new puzzles by nibbling at the pieces!
No peeking! Tell your child to close his eyes, then fill a bag with items you've got in the car: a cup, a toy, a sock. Let him feel inside the bag and guess each object.
Twisty creations Pack a bag of pipe cleaners. What contraptions can your child invent?