I served in the Army as a Combat Medic, and I would always carry several on the outside of my aid bag. As Kcarf has stated the use of them as a last resort has changed. When I was in medic school in San Antonio Texas, I had a Special Forces Physician Assistant teach the Combat Medic side of our course. This was in 2004, he said he was always fighting with the conventional side with the hospital at Fort Sam. He taught us to use them first, and if we were busy setting it up we would use a knee to compress the artery to slow the bleed in the meantime.
You need to learn how and where to apply a tourniquet. You want to apply in maybe 2 inches above the laceration/amputation. You don't have to worry about losing the limb because of blood restriction for several hours, however before then the person could incur some nerve damage. When you apply it you want to make sure it is not over any clothing as clothes can cause the tourniquet to slip especially if they are blood soaked.
For a fracture of the femur/ thigh bone it is in fact possible to bleed to death internally with no outward sign of bleeding. With that type of break the muscles will retract the lower part of the break and it is possible to shear the femoral artery so in that case after 911 is called or you have more than one person around you want to apply manual traction and keep it on there until EMS arrives.
If you guys don't care to walk around with a medical grade tourniquet on your person, I would suggest a large bandana or two and pen or flash light for tightening down on the limb. The second bandana one would be used to tie off whatever you used for a stick to stop the bleeding. Always think multiple uses for the items you carry as you can only carry so much.
You also want to make sure you physically write a time on the person with a marker as to when you applied the tourniquet. We would write a time on their forehead like this for example "T-15:00 or T-3:00PM". The newer tourniquets have a place to write on them, however blood could obscure that or take off the ink.
Lastly I would suggest those interested in advanced First Aid should take a class at their local community college. You can become an EMT-Basic in one semester, and the knowledge you will learn is empowering.