Here's my little trick I came up with years ago. Pull a pen or pencil out of your purse and let the kids have a ball drawing all over the exam table paper. They have to roll out new for every patient so they're going to throw it away anyways, might as well make it pretty while you wait. We've practiced letters and drew pretty pictures but what always makes me smile is when they choose to trace their hand. When they are really little, too little to draw themselves but are starting to lose it from waiting, I would trace their hands to entertain them. My children hardly ever trace their hands when coloring at home but almost every time they draw at the doctor, a hand print shows up! Cute.
Next time you're waiting give it a try... but once you've done it once, don't EVER forget to have a pen in your purse, you'll be sorry!