Place all of your equipment on top of the pre-cut grid. Distribute until you have a suitable arrangement. For ultimate security, be sure to include a two-inch margin around your valuables.
Remove the foam according to the shape outline by plucking it with your fingers or use a cutting tool for a more precise contour. Several tools allow you to effectively cut the foam: kitchen knife, exacto knife, hot wire cutter, electric knife.
Once the foam is cut, place your equipment back to check that everthing fits. Adjust as needed if necessary.