This is a variation on the pendulum expression.
Keyframes were applied to Jack's position at frames 0 and 1 to move him out of the box. Then this expression was applied to the position property to give him the bouncy motion:
veloc = 35; amplitude = 30; decay = 1.0; y = amplitude*Math.cos(veloc*time)/Math.exp(decay*time); value + [0,y]
Adjust the velocity, amplitude and decay parameters as needed.