Unpowered Coaster Car!

In engineer class we were asked to present an "elevator pitch" for our unpowered coaster cars. I chose to design a simple light weight coaster car because I felt it'd be more efficient. As the chassis, I decided to use a foam container that is often given to an individual after ordering chinese take out. I felt this was best because it'd be light weight and wouldn't weigh the wheels down, perhaps giving it more velocity. I felt using straws for the bearings would be best because it's secure and it isn't costly. It'd enable the wheels from falling off, stabilizing the car. Each one of these parts are significant because if one was missing, the entire car would be defected and would be unable to reach the objective, which is rolling down the ramp. I believe placing two CD's on each side of the coaster car would be the most efficient position because it'd be well stabilized on both sides. Keeping the design simple is essential; as long as the constraints and criteria's are met and the coaster car is able to roll down the ramp securely the design is fine, there's no need to complicate things.