Re: [heavy] a few grams which safe lifes
In a pinch tourniquets can be made of just about anything: rope, neckerchiefs, belts, even parachute line (you'd want to use multiple strands to broaden the surface area) coupled with a pen, sharpie, screwdriver, or stick to twist the material and apply tension should do the trick, then just tie or tape it off.
Most emergency trauma first aid is not rocket science. There are multiple 10-20 minute videos on youtube that show how to make a traction splint out of sticks. Here's a pretty good one: https://www.youtube.com/watch?v=vWzYAswEWko
Off hand, I would also recommend brushing up on CPR and spinal stabilization techniques, wilderness stretcher building, and emergency trach procedure ( http://www.tracheostomy.com/resources/surgery/emergency.htm )