The number of yoga books has grown at pace with the explosion of students, teachers, and studios over the last decade. (Who hasn't investigated yoga in some way over the last few years?) So what makes new book Yogabody stand out from the pack? It gets to the true understanding of how to connect the mind to the body when the body—the anatomy and kinesiology (the science of movement)—remains somewhat of a mystery.
According to author and restorative yoga guru Judith Hansen Lasater, “You can’t fully understand the dynamic movement of asana without first understanding the basic structure of the human body.” In Yogabody, Lasater illuminates the body in parts: the locomotor system, vertebral column, lower extremities, the trunk, and the upper extremities. Her straightforward and thorough descriptions are complemented by beautiful and well-labeled color illustrations, and her “Experiential Anatomy” segments encourage deep exploration of joints and muscles through basic postures--a fantastic resource for the dedicated practitioner and new teacher, who may feel awash in information.
Though the addition of a glossary would have made it a go-to yoga anatomy and kinesiology reference, Yogabody stands as an essential tool for awakening your body through well-informed asana, empowering you to take charge of your own yoga practice. If you're a yogi who's ready to take your practice to the next level, dive into this one.
Get it: amazon.com

In other words,which constant companion could you just not live without? Vote now!
We have a "kit" that goes with us in the car if we'll be in for any amount of time. It definitely cuts down on the 'are we there yet?'s
The most important thing is to bring enough little things for them to do to keep them busy. Bring small games, puzzles, crayons & coloring...
I say bring a doodle-pro or lots of color wonder markers & paper.