Most of these legends have rational roots.
For example, just out of the top of my head:

1. What about snakes then? All those REI snake kits are complete trash with their suction caps? Poor Indians, they had no cellphones nor the helicopters...

4. Not every oil will help. The sea-buckthorn oil is the best heat/acid burns cure known for centuries in Russia. Far outperforming any over-the-counter synthetic stuff.

5. Raw Steak is the same thing as ice - for cooling. I doubt anybody thought of a hot steak for that. You'll get it from a freezer right? Your eye will swell while you'll be looking for ice, zip-lock, and towel and putting them together. The faster you get it cooled the better the results. I'm using a steel spoon quite effectively. And the bacteria story is some medieval fairy-tale.

6. I like peroxide! It seals the broken capillaries instantly. So no under skin bleeding occurs at all. And it definitely kills any germs faster than soap or any PG based ointment. Sure thing a small scratch doesn't even deserve such a treatment.

It's seems to me that above mentioned guide was cooked by a private clinic manager or a backyard hiker.

Very much true. This is a point used for thousands of years in Chinese medicine to treat any pain in the face, gums, headache and pain in general.

Here's a well known Army medical myth, even though all the medics believe it.

Motrin cures all ills. It will cure headaches, the common cold, reduce swelling, regrown severed limbs, and even decapitations.

Not really, but it seems that way sometimes.

As for bone "setting," don't do it. Immobilizing, please do! I've never seen anyone screaming in agony from a broken bone, and I've splinted A LOT. Moans, cursing, "owowow...." for a few seconds. There are a few fractures I hear that hurt like crazy: femur, pelvis, though the only femur I ever saw the kid was surprisingly calm. These folks might scream. The main reason to splint, though, is to keep the bone from moving. Why? Every time that bone moves, the jagged edges are ripping muscle, tendons, the periosteum (it's kind of a skin-like membrane that coats the bone, and full of pain fibers). Also, those edges can cut blood vessels. Did you know you can lose over 2 liters of blood in a femur fracture, and over a liter if you break your forearm? So, tell them to tough it out for about 2 minutes.

With wound healing, recent studies HAVE shown peroxide to kill fibroblasts, which are responsible for repairing the wound. Not sure how much it'll slow healing, but just a heads-up.

As for my top 5, seen over the past 10 years:
1) Black pepper in a wound just makes it dirty, not stops bleeding.
2) Don't ice burns. Cold water, compress, NO ice or butter!
3) People putting a tourniquet on a bleeding finger. Do NOT use below the elbow or knee!
4) Hyper-panic parents. Just plain annoying. If you kid was that bad off, why did you drive 10 miles to the hospital instead of calling 911? Or why did you wait a week before coming to the ER (my personal pet peeve)?
5) Yelling, "Damn it (fill in name), don't die on me!" while simultaneously slamming your fist into their chest is MUCH more effective than CPR, medications, or a defibrillator.

Which brings us to another first aid "myth":

Getting kneed or kicked in the groin DOES NOT make you forget about the original ailment; it simply adds to the misery.

Only if you don't manage to pinch the venom sack while doing it. Doing so will do in a hurry what its already doing slowly: Pumping the contents through the stinger into you. Tweezers, SAK pliers, real needle nose pliers, or any stiff object is better for getting them out.

In the article I referenced, the researchers mention this common advice as one reason to test out the difference between pinching vs scraping because they say that the anatomy of a stinger (including the attached venom sac) does not support this commonly held belief. Their results seem to confirm their skepticism that pinching and grabbing the stinger does not increase the amount of envenomization, so however you get the stinger out, do it as quickly as possible and don't waste time trying to find a credit card, tweezers, or other scraping tool.

Jellyfish and sting ray venom, from what I've heard (careful now) can be neutralized by immersion in very hot water. The proteins in the venom are denatured by the heat.

For bee/wasp stings, meat tenderizer, which contains papraine (sp), can take the pain away quickly.

So. What's the most readily available hot water at 100F on the wild beach?
Another "myth" turned to be a reality.
http://crc.hawaii.edu/studies/crc00-03.htm

Ok. Some more:

3. Drinking Booze to Ease a Toothache
...it'll ease everything almost the same way as any narcotic. Just take enough

7. People May Swallow Their Tongues During a Seizure
Someone has a seizure and a passerby sticks something in the patient?s mouth so they don?t swallow their tongue

...not SWALLOW, but BITE it off! So use a stick or something if possible.

Toothpaste is supposed to be good for bee stings. See eg http://www.slate.com/id/2088863/