Medic ropes are a simple and effective way to simulate combat casualties and to keep track of how many lives you have left in a milsim environment. They are quite simple, any rope or cord will do. I find a length of 12-18 inches to be an ideal length. I like to keep my medic rope attached to my load bearing equipment but some keep them in a pouch or pocket. Prior to the beginning of a game, tie a knot for each life that you have. When you get hit, a medic can simply untie one knot. When you are out of knots, you are dead and must respawn at the appropriate location.