You can use those bags and other antistat materials to make a simple force sensing resistor. The best ones come from using the conductive carbon impregnated foam material. Just sandwich some foam between a couple of metal plates or bare copper PCB material and measure the resistance between those plates on your multimeter. Press on the stacked material and watch the resistance drop and then go back up when you let go. It will never calibrate to be a useful scientific sensor, but it's good enough for some simple and fun analog projects or even Arduino things.