I am, among other things, an army surgeon. I am thus also tempted to bring a lot of stuff with me in my medical kit (if nothing else, it is a hell of a lot easier for me to stock narcotics) but I do try to restrain myself. I manage to do without a needle driver and 3-0 silk, as much as it makes me feel naked.
A 5x9? That's rather large, isn't it? I guess someone might get an open fracture or something, but then you're likely to improvise a dressing out of clothing, anyway. Such a wound would certainly justify ruining your $80 jacket. By far most wounds on the trail are tiny, and just need a 2x2, but a 4x4 (as you have) is more versatile and can be cut down to size. I carry real gauze because it is more versatile than those fake-gauze dressing sponges.
CPR barrier? Well, as you say it is very light... But it is also low liklihood of use, and probably not realistic to expect a save if you are far from an AED. Well, maybe my view is skewed a bit, as most of my codes are traumas not cardiac. Your call. But I'd say just keep your immunizations up to date (especially hepatitis) and know your hiking partners.
Quik Clot?!? Where are you hikng? Iraq? I'd wager that on the trail a massively bleeding wound to something that won't take a touriquet (trivial to improvise) is rare. I guess you just have to do your own risk-assessment, though. And even then I'd recommend one of the chitin dressings (such as HemCon) over Quik Clot. HemCon's are expensive as hell, but you are much less likely to injure the patient than you are with Quik Clot. Quik Clot is VERY exothermic. (And a pain in the a$$ for the surgeon to remove later...)
Conceivably you could do with one pair of gloves. Make the assumption that if you need more than one it will be treating the same injured guy until you can get him to safety, store the one pair in a ziplock (that you brought food or something else in) and reuse it. It is for your protection, after all, not his.
It is low likelihood of being needed, but I carry a 14g, too. It is lightweight insurance against tension pneumothorax if anyone takes a fall, and can be lifesaving. I'd hate to lose anyone to something that easily fixable.
Alcohol AND iodine? If you use an alcohol stove you can do without either, and just use your stove fuel. (This was a nontrivial influence on my choice of stove design.) Or use Purell, if you carry it. Purell is also a handy emergency firestarter...
For multi-use antibiotics amoxacillin is a pretty good one. Many will work. Fluroquinolones are handy, too. Just pick a favorite, and try to tailor it to your location. If you are going someplace exotic I find that the Infectious Disease fleas can be amazingly helpful, and actually quite interested. (Mefloquine Mondays, anyone?)
I keep telling myself to remember "I am not a walking tertiary care center." In the field I do not have an obligation to provide definitive care. I just have to get them to EMS alive.
That said, if I am to be the "medical guy" for a large group of people I don't know very well I tend to bring a LOT more stuff. E.g., anyone who needs an epi-pen should be responsible enough to bring his own and attach it to his pack strap where others can see it, but there are a lot of idiots out there. In such groups I also tend to bring aspirin for AMIs. (Otherwise I bring only 800mg Ibuprofens and 650mg Acetaminophens, so I can double-dose and walk out on a sprained ankle if I must. In truly remote areas I bring a couple of Percocet, for the same reason.) I haven't yet brought my own nitroglycerine, but I always think about it, and I might if I was in a large group in a very remote part of the world. Then I could at least give half of MONA therapy. Hmm, would Percocet count as "M", and let me give 3/4? I'll have to look that up.
Again, my world view is colored by my experience, so I tend to think of trauma. There are several injuries that will kill you quickly, but that are easily treatable in a trauma bay. (Emphasis on "in a trauma bay.") Various lists exist, the "7 Killers", the "Deadly Half-Dozen", etc. I'm sure that you have been taught to think of them. Forgive me if my list differs from yours, but I'm trained to think about these things differently than you, so I haven't looked this up in a while:
Exsanguination: This is your Quik Clot or HemCon. I maintain that they are low-utility, and improvising a tourniquet is all you have to know. For a solid viscus injury or other internal bleeding, activate the EPIRB and pray. Have you been taught permissive hypotension, or are you an old-school IV fluid guy? I'd recommend learning permissive hypotension for field medicine. For a pelvic fracture, sheet the pelvis. This is another injury that justifies ruining your $80 jacket.
Airway Obstruction: The knife on my Leatherman Micra is damned sharp, and I have hydration tubing, for my crichothyroidotomy That's the best that I think I can do without hauling a code cart with me.
Cardiac Tamponade and Tension Pneumothorax: There is no body cavity that cannot be reached with an 14g and a good strong arm. I would not recommend that the laity try to do a Pericardiocentesis, but I would sure give it a try as a last resort. Any monkey can learn to do a Needle Thoracostomy just by googling it. (Diagnosing the tension pneumothorax, on the other hand, is a little tricker for a layman.) See, that 14g is multi-use! :-)
Open Pneumothorax: Some tape and almost any reasonably flexible piece of plastic can improvise an occlusive dressing, or better yet a semiocclusive dressing with a flutter valve. So, leave the labels on your water bottle. Or use the cellophane from a pack of cigarettes. I wonder if silnylon is airtight enough to work? Tyvek certainly is.
Hemothorax: Hmm. EPIRB and prayer, again? I guess if I was sure of my diagnosis I always have that knife and hydration tubing to improvise a Tube Thoracostomy, but I wouldn't recommend it to the laity. Who cares about the resulting empyema if you can save his life? Some jackass might decide to sue you, though, so he'd have to be nearly dead before I'd do this. Improvise a Heimlich valve from the finger of your glove.
Flail Chest: Definitely EPIRB and prayer. Usually these are caused by MVAs, and the only wilderness scenario I can come up with is a long fall. In such a case you will probably have more pressing problems than the flail chest. There are those who advocate wrapping the chest, but this really doesn't work and causes a lot of pain, thus leading to splinting and even worse oxygenation.
Another thing you will see on some lists is a Subdural or Epidural Hematoma, but I really can't think of a realistic way to do a burrhole in the field. Nobody really does them in trauma bays, either, for that matter. The neurosurgeons can get them into the OR pretty quick. I guess if I was on-call in some sleepy rural hospital with the nearest neurosurgeon hundreds of miles away I'd give it a shot. I know approxmately where to stick the Black & Decker, after all, and he's going to die anyway, right? But the weather would have to be REALLY bad to preclude a helicopter flight...