All weapons and max ammo
At the Plant Electrocution - level 2, slide down toward the holes in the ground. Go in the second hole. Make sure that you slide into the hole and try to slide toward the lighted area. Pick up the items (the key). Now use the grapple to get out of the hole and finish your slide. The key is for the door beside the vines behind the glass. Go in the door and fight the plant man. Beat him and you will get an envelope with the letter C on it. When you finish the game this will activate the cheats.