Mix 2 parts water to 1 part rubbing alcohol in a large Ziploc freezer bag.  Keep this in your freezer and it will become slushy.  You may re-use pack again by refreezing it.  When ready to use, wrap a moist warm towel around cold pack and place it directly on your skin of the affected area.  Leave on for 10-15 minutes or until your skin gets numb.  Consult with your therapist or health care professional before using a cold pack for a particular condition or injury.