Go to Walmart in the hunting section and find the hand warmer and foot warmer foil wrapped packs. Just a couple bucks. They last a few hours and are air activated when you open the package. Normally you put them in your boots or gloves to help keep your hands and feet warm but you can just use a rubber band and wrap it around your specimen. You also can make your own delivery system if you have access to medical supplies. IV bag with exit tube attached works and clamp on end works.