The crystal. I do not think it should not be rigidly mounted to the board. It has a mechanical element. Shock could ruin it. I picture that it should be mounted it on a foam standoff, 1/16 or 1/8 inch high. Use non-metallic line wrapped around it, and tie it to the board. Make the leads very thin, and slightly flexible if you can, so they do not transfer sudden acceleration to the crystal element.
How to test a board for shock? A paint mixer applies continuous shaking. A cheaper method is to bang its edge with a hammer. I have no idea what G-force this is equivalent to.