Going someplace where you might need that knowlege? There are rescue sleds in the Chalet at Wirth and most of the trail centers in Three Rivers Parks, just FYI. I could show you have to rig up something using a packframe and pack bag or a tarp and skis. One avy shovel won't give you enough space to adequately support somebody with a back or neck injury.
My other suggestion would be carry on of those roll-up plastic kid's sleds attached to or in your pack. They cost less than 10 bucks, can be rolled up to less than 4 or 5 inches wide, and can be used with or without rigid support in an emergency. In EMS/Rescue we have a similar, longer device called a "Sked." You can also get them at Gander or Cabelas for draggng your deer out of the woods. (A lot cheaper than the Sked, too!)
Come out to Sand Dunes some time when the snow comes back!