Please don't construe anything I write here as advice, just to add to the discussion. I'm only giving you the advice I got over the years that I was adventuring. A good bit of it was as a caver and a good bit of it was for situations underground where keeping your kit to a minimum was essential if not existential. I also backpacked and canoed for 30 years before age caught up with me.
1) Forget suturing. If it's that deep, your big worry is sepsis.
2) Tourniquet? Expect to lose the limb if it is that bad and you're that far out. Use pressure wherever possible
3) "Fortunately the vast majority of first aid needs, not involving serious thoracic or abdominal trauma, can usually be addressed with kit on hand. A shredded shirt as bandage, magazines or branches as splints, foil or plastic wrap (sandwich baggie) to seal a sucking chest wound." -- This. +1
4) Buddies get out. Loners end up as mulch.
5) Staying warm and dry is always Job 1. Hypothermia is always a possibility. Carry a large plastic leaf bag and some plumbers candles and learn how to use them. I've seen this save lives above ground as well as below.
6) Shock kills. Apply your emergency blanket before you need it.
7) If there is any injury or malady that gets you asking: "Should I keep going?" It is already becoming too late. Get out.
Fortunately, I only actually had to follow this advice a couple of times. I got concussed once underground. I had a couple bouts of hypothermia. I had to turn around once on a backpacking trip and wobble out on one leg. I had sepsis in my hand once. Overall, I stayed safe, so don't count on me as being experienced in first aid kit assembly.
I will say that the absolute best thing I've had to go to over the years is the tube of triple-antibiotic salve with anesthetic. That's helped many times. The other thing that's helped is having a Swiss Army Knife with a small blade that I could use as a scalpel-- that and the tweezers have been really helpful in things like nasty splinters. I also can't count the number of Ibuprofen I've sucked down on the trail.
Always leave word with someone where you'll be and when you're due out. Always set a time when you've either called in or they need to call someone. Always give the number ahead of time. It may be the local sheriff or somebody else. However, make sure they know what they are doing. As a caver, we never got 911 involved. We had an 800 number to call for underground emergencies and that number brought in a team standing by with a plane that was prepared for it. Whatever the situation, know who to call and tell your ground crew.
