Do not turn off your lights!
You mean besides the Spear of Longinus, which could cause empires to rise and fall?
There’s Ascalon, the lance (or in some versions, sword) that Saint George used to kill that dragon you might have heard about.
There was Joyeuse, the sword of Holy Roman Emperor Charlemagne, which was said to contain bits of the Spear of Longinus in its pommel.
Charlemagne’s paladin Roland had a sword called Durendal, which had in its hilt one of St Peter’s teeth, St Basil’s blood, a hair of St Denis, and a scrap of cloth that belonged to the Virgin Mary. It was said to be the sharpest sword that ever existed. (As long as I’m naming swords from the Song of Roland, Ogier the Dane’s magic sword was called the Courtain, and Almace was the sword of Turpin, Archbishop of Rheims.)
Saint Ferdinand III of Castile had a legendary sword called Lobera (“the wolf slayer”).
There’s the sword of Saint Peter, which he used to cut off the ear of a guard who came to arrest Jesus before the crucifixion, but it’s legend is not particularly badass, except in some legends it was given to Saint George, which is pretty cool except obviously he killed the dragon with that spear I was talking about a few paragraphs ago.
There’s the Sword of Mercy, which belonged to Edward the Confessor. It’s a sword with its tip broken off; it’s said an angel broke the tip off to prevent a wrongful killing. The sword remains today as part of the British Crown Jewels as a symbol of regal mercy.
More Judeo- than Christian, but the Seal of Solomon was a magical ring that King Solomon used to summon, control, and imprison demons.
There’s a few, anyway. I know they’re mostly swords, but I’m not aware of any Blessed C-4 out there (please do not say Holy Hand Grenade, nerds out there). Some of these might be of dubious Catholicity, but they all at least have something to do with a saint or a relic, so there you have it.