No matter how large or well supplied your FAK may be, if the emergency is great enough (just consider the current Montecito mess just up the road here in SoCal!). At some point you will need to depart from protocols to some degree, make something up on the spot, and take measures to deal with the situation.

An example from my experience: We were on a pleasure climb, a long time SAR colleague, myself, and a friend of his. We ran into a guy who had been hit in the head by rockfall, with obvious cranial trauma. At that our companion was an MD, with three years experience in the local ER. Treating our victim, we realized that we needed a cervical collar, given the high probability of occult neck trauma. We shortened my 3/8" blue foam sleeping pad by 5 or 6 inches,folded it over, tastefully allied duct tape, and voila! a C-collar.

At least it worked well enough in the subsequent evacuation.

Splints, especially, are often improvised. What would you recommend for improvised, reasonably adequate, measures to deal with situations?