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?

In the Wilderness First Aid course, improvising a C-collar with a sweater, or an arm splint from a magazine would demonstrated and then practiced. The WFA instructors were big on improvisation, a necessary skill when you are a great distance in time and miles from a medical facility.

Good stuff. I have taking Wilderness First Responder on my bucket list.

to me, all first aid is improvised.

Large blanket pin to keep the airway open in transport. Thru the tongue and lower lip.

Ice Axe traction splint.

Webbing for outside the boot ankle support.

Hard hat wash basin.

Warm wet black teabags for eye infection.

Campfire charcoal for upset stomach.

Salt, water sugar for oral rehydration solution.

"Large blanket pin to keep the airway open in transport. Thru the tongue and lower lip"

Most of your recommendations sound good. But I suggest that you avoid the first. Find another way to accomplish the task, without solutions that involve cruelty. I understand that EMT's are often so "training oriented" that it becomes a strange type of fixation, and they forget to be human beings. I can think of ambulance crews I knew, when I did my own EMT training. And they would sit around and laugh at doing intubation on conscious patients, who were tried down, immobilized with restraints, and then had plastic shoved down the their throats by the EMT's.

Personally, I'd rather be dead. Than to put up with "EMT waterboarding". But it's a reality out there.

My constructive suggestion - find a better solution.

BTW, it terms of improvisation.
always seemed to me that pieces of thick cardboard were really helpful. but you need them to be long. maybe 3 feet long. you can bend cardboard (down the axis, lengthways), and use duct tape to wrap it. and it's excellent for building splints very quickly. The nice thing about cardboard - very easy to cut with scissors. So you can shape it - to your own purposes. also, if you don't use it for EMT purposes, you can always burn it as fire material.

the main disadvantage. it's useless if it gets soaked with water. if there was such a thing as "water-resistant" cardboard strips, it would be nearly ideal.

It was part of an Wilderness EMT training. Most groups I worked had airways in the first aid kit tho.

How would you improvise an airway?

Improvised airway - Simply reach in and pull the lower jaw forward. Turning the victim on his side (provided there are no cervical issues!) is also recommended.

Quote from Wilkerson's Medicine for Mountaineering, 3d ed., p.49

"insert a large safety pin through the meaty part of the tongue and hold the tongue forward by taping the pin to the chin or anchoring it in a similar manner. Although this technique sounds and appears brutal, it is simple, highly effective, and produces no permanent damage."

Emergency medicine is often not rated PG....

And just to think, people actually pay to get their tongues pierced, when they can be having a 1st Aid attendant do it for free.