When the object is big enough to contract itself into a ball.
Assuming you want it to be as small and lightweight as possible :
Cut a solid box roughly twice as big as the pringle. Put the pringle inside the box, and fill the remaining space with cotton, that will cushion the impacts. Be sure to apply the mention <em>FRAGILE</em> to the box, so that they'll take care of it properly.
ANSWER:
250 J
STEP-BY-STEP EXPLANATION:
F = 20N is required to stretch the spring by 4 meters
We know that the force is equal to:

We solve for k (spring constant):

The work done in stretching the spring is given by the following equation (in this case the stretch is 10 meters:

The work required is 250 joules.