Superman has a shocking weapon hidden in his belt
With his own twist on one of Batman's most iconic pieces of gear, Superman has a secret weapon that will surprise almost anyone.

Given their longstanding friendship, it's no surprise that Batman and Superman managed to learn a thing or two from each other, with a secret weapon on Superman's belt suggesting he learned from Batman how to always be prepared.
Superman is without a doubt one of the most powerful heroes in the entire DC universe, able to consistently punch and kick titans like Darkseid or Doomsday. With so many powers including flight, invulnerability, x-ray vision, heat vision, super strength, super speed, and super hearing, it's hard to think of an ability Iron Man doesn't have. But all of that power still pales in comparison to the power of preparation, and that's what Superman seems to have learned from Batman. Whenever Batman has to go up against someone stronger than himself, he's always ready to exploit their weaknesses, as seen when Batman defeated the entire Justice League.
In Jeph Loeb and Michael Turner's Superman/Batman #13, Superman finds himself up against a fallen Superwoman who is currently enslaved by Darkseid. Superman reasoned with his cousin to no avail. End the fight. It should come as no surprise that Superman and Supergirl find themselves evenly matched when they go head-to-head. As incredible as Superman's strength is, it's nothing compared to Supergirl's power to make her a monster. With no other choice, Superman suddenly unbuttoned his belt and pulled out his secret weapon, a kryptonite ring. Using this ring, he can take down Supergirl with one punch. Considering that Superman's best friend is the perpetually paranoid and ever-ready Batman, it makes perfect sense for him to have this weapon on hand.
Superman Learned From Batman On Being Prepared

Superman is used to dealing with villains on an unequal playing field. In Superman's rogues' gallery, there are very few villains who can truly match him in speed and strength, and very few more can. While Lex Luthor is undoubtedly dangerous, he can't physically fight Superman on flat ground, nor can Metallo or Parasite. The biggest threats Clark faces are usually other Kryptonians, since they have all his strengths, but also his weaknesses. However, there is one major difference: Superman is used to working with kryptonite, since villains like Lex and Metalloo use it Widely. While this would weaken him, Superman actually needs Kryptonite, as it's the only solution to the evil Kryptonians. Evil Kryptonians are unlikely to encounter kryptonite themselves, as the substance is so rare that it's unlikely anyone would use it against them. Because Clark is exposed to it so often, he may have developed a degree of resistance to it by now, allowing him to use it as a surprise weapon against any evil Kryptonians he encounters.
Raw strength and strength can only get one so far. When confronted with villains who can match his strength, Superman needs to be able to outsmart them, and thankfully, Superman seems to have learned from Batman how to be ready for battle.