Carrying a "backboard" is not so important and long term immobilization on a hard surface can have unintended consequences as mentioned above.
Im not going to get detailed here, but i think the important thing is to be educated enough to recognize when someone in an event has been exposed to and possibly has experienced cervical/spinal trauma.
Now, if your in the middle of nowhere and no-one is going to help you and your hurt friend- are you going to sit on your *** and let them die cuz you are worried abount moving them? You going to stand them up and do jumping jacks down the trail to the highway when they were unconscious a few minutes ago after a cartwheel rollover in their jeep? What if you are now exposed to environment such as wind, snow, heat? You staying there till someone helps you out of your situation?
No. Your going to take care of yourself and safely get your buddies to where they need to be. Call a heli? Great, what if its snowing. blowing, and night? Wait for SAR? Got a full day.
Learning to recognize real injury by training- CPR, 1st aid, EMT (this should be mandatory in high school), Woofer, Medic, etc..., then take the precautions needed for the circumstance.
You could very easily fashion a makeshift board out of anything- roofrack, shovels tied together, dare i say a snowboard or skiis, maxtrax, rolled in a mattress/sleep pads. Perfect, ideal, no. But could save lives. Pad it heavily and roll towels to wrap their head tightly, duck tape or tiedowns to hold them to it securely but dont cut off circulation. One could even securely pack someone into the backseat of another rig in a fashion that would provide a ton of immobilization to the spine, pelvis, chest, etc...
Most trauma care is common sense and protection from further injury.
The idea here is that if you are forced into a position to take care of yourself or others, you must rely on your abilities to think outside the box. that is what being self-sufficient is all about. You cannot prepare for all events, but must be able to overcome the obstacles in front of you.
Train to help people not harm them. Learn to assess and then treat basic injury, recognize serious life-threatening injury. Even if you dont have the skills or tools to treat. Its up to you if you think this person is too seriously injured to move them with the means you have avail., or if its too serious of a situation you are in to stay and wait for help.
Opinions only here