I was trained that if you use the tourniquet, that limb will be amputated. It's not to slow blood flow so it coagulates, it's to block blood flow to prevent death by exsanguination. In that case you can use anything - a belt, rope, necktie, scarf, strap from a purse or knapsack. Anything. I was taught that a tourniquet is the last thing to go in a kit, because it can be replaced by so many things and you will probably never use it. Better to put in more gauze, gloves, and tape.