Before taking a long fall, pull the pin on your grenade and hold it while you drop. If you time it right, the grenade will finally explode in your hand just before you hit the ground, and then any damage that you take from the fall is measured according to your position when the explosion occurred. That means that you can now survive a much longer fall than normal, provided you have enough life on your meter before you drop. Of course, the damage you take when the grenade explodes is substantial enough that you still have to get the timing just right.