The most important item to bring when you are going to kill these monsters is your rockhammer. Without it, they can not be killed. Besides your rockhammer, you should bring either food or prayer potions. Another important optional thing to bring is high alchemy runs. This will save you quite some inventory space since these monsters drop quite a lot of alchables.  Another important thing to bring is a weapon that has a crush attack and a decent crush bonus. Using a weapon like that will make sure you can kill them a lot faster. One of the best weapons for this is the abyssal bludgeon. This weapon is quite expensive, but it isn't an absolute requirement. You can also use a whip, while it has slash as its attack, the defense of a Gargoyle is not high, so it kills them pretty easily.