Step 1: Materials.
Who said 2 wrongs don't make a right? Rather than throwing out those evil plastic bags and non-biodegradable styrofoam peanuts you can reuse them to save energy.
Simply fill one plastic sack with peanuts and then use another bag to cover the gap making a Styrofoam pillow. You can double-bag or use plastic bags as filler also. Seal the ends with clear packaging tape and your done. Make enough pillows to fill the unused space in your freezer or deep-freeze.