High end composite flywheel rotors can achieve nearly a kWh/kg of rotational storage when magnetically levitated in a vacuum chamber. Consider mounting a flywheel in the middle of a wheel, such that magnetically decelerating the flywheel accelerates the wheel. Even if the flywheel was only 1% of the system mass, that is 0.01 kWh/kg, enough energy to accelerate the entire system to 600 mph. Lots of practical system engineering challenges, and drag would consume more energy, but It would be amusing to outrun a top fuel dragster with a wind up toy.