We chose to carry this robot kit because everything you need is included in it.
From the manufacturer:
Robotics and industrial automation are everywhere these days. Robots help build, package, and ship everything from your breakfast cereal to your car. With that in mind, we designed the ScoutMakes Robot kit to help those with an interest in robotics learn the basics. With it, you will create a simple, wheeled robot while developing a familiarity with concepts like mechanical assembly and motor control. This kit also includes a piezoelectric buzzer and NeoPixels that allow your robot to play sounds and glow while it’s moving around.
And, thanks to the included Azul board, you’ll be able to send instructions to your robot, over BLE, from an app on your iOS or Android device. To control it, you can simply tilt your device in the direction of travel.