I do a lot of Wilderness and Trail, Search-Rescue. Rarely, in SAR, do we improvise for patient stabilization. It would have to be something that we're just absolutely not prepared for, at all. Perhaps multiple patients. It's hard to pack in with short manpower, and inability to determine needs with no other information than "Person Lost" or "Person Down". I think of a six man crew, as a walking rescue truck and ambulance. Everyone, whether it's chest pain or a rolled ankle, gets a backboard, so they won't fall out of the rescue basket if we have to transverse something. As for materials, you're limited as to what you can carry, vs what you want to carry. The traditional EMS style splints just don't work, the boards, framed devices, etc; there just isn't anywhere to store it. If they tell us, it's a fall victim with a femur fracture, we'll carry in a HARE or REEL; or MAST.. Whatever the info is. If there isn't any info, we just take our medical bag. You can't have enough SAM's. I hate SAM's.. on the street. They bend too easily. I'd rather use one of those "FOX" Full-On Extremity Splints w/ the padding and velcro straps. But in the woods, you can use them for anything.
Fracture kit;
1 x KTD, Kendrick Traction Device. It's a folding traction splint in a pouch, made for the military, great for SAR. It employs the same theory as using a ski pole for a traction splint.
10 x SAM, 36" x 4"
5 x Extra Large SAM, 36" x 5"
20 x Cravats
2 x "X-Collar"
4 x 3" Elastic Wrap
4 x 4" Elastic Wrap
2 x 6" Elastic Wrap
A shit load of 3" VetWrap (The cheap version of Coban, still made by 3M, but sold at Tractor Supply for $8 less than moore medical sells the exact same thing)
Dressings, bandages, etc. Loads of stuff, in a nice, easy to carry back pack. Everyone always says they can't find our "EMS Pack" in any catalogs. EMS. Eastern Mountain Sports. Sarcastically cute.
If it's open, the fx, irrigate, dress and wrap with the plastic from a large dressing; then wrap again and splint. It's gonna be a bitch to extract someone, without SAR, if they have an open fx of a leg. An arm, you're probably okay, a leg, no way.
Straight sticks, clean the bark off, make sure they're not infested w/ anything; wrap in clothing if possible. Like slice the toe end of socks open, and slide the stick through it, esp. if there's any wounds. You can, in theory, of course, put anything over the splinting device if it "should be clean". You can use condoms if you have to, why you have enough to do that, we'll never ask. Camping should be fun after all. ha ha. Pack frames can be bent, some have rigid inserts, long slats of bark, with strips of a shirt.. The sky is the limit, use "KISS", Keep it simple stupid.
You can't always be prepared, as a hiker; but we're expected to be reasonably prepared; so if something looks like it could work. Use it. You really can't go wrong, when you have to create your own options. Well, you can go horribly wrong, but you never know, till you try.