7. Giant Penny
This classic prop comes from one of Batman’s battles with one of his darkest, most iconic villains: the Penny Plunderer. After the Plunderer began targeting Gotham City, Batman determined that he would hit the local coin exhibition. The exhibition had the first one-cent stamp in history there in addition to a giant penny so it was an obvious target. So, Batman stopped a criminal from stealing the penny and then essentially stole it for himself. We never see Batman take the coin or how he gets it into the cave, but ever since their confrontation the penny has been a staple of the cave.
There have been a few instances where super villains get into the cave and try to crush the hero or some of his tech with the penny. The most famous instance of someone using it against the Caped Crusader came during the Knightfall storyline. Bane shoves Batman into the penny so hard that it loses balance and comes crashing down on the hero.