So...here's my 2 cents on trauma kits. I've been in EMS in an urban setting for almost 10 years. We carry tourniquets. I have never used one. I think, this is just my opinion, that they are good when needed. I've run lots and lots of shootings, stabbings, MVCs and I have always been able to control bleeding on an extremity.
I have seen bystanders (even some police officers) use commercial tourniquets, but on injuries that it did not need a tq. The military study quoted previously, much of their data came from blast injuries (which is a whole different ball game).
As far as combat gauze or quickclot, we don't carry it. Quick clot has exothermic properties and can cause burns and contaminate the wound. Trauma surgeons don't like it. Combat gauze does not cause burns, and is a little better in my opinion. But, if you use either of those, remember just because you stopped the bleeding externally, they are probably still bleeding internally.
With that said, I do carry a tq in my bag. I carry gauze and ACE wraps (for a pressure dressing). Bandaids, gloves, duct tape, alcohol wipes, and a large bore needle for chest decompressions.
If I was way out in the woods or in the middle if no where, I might add combat gauze or the like...