Storm Raiser -
A sword/ trident (Just like Jason's sword/spear coin) that is made by elder cyclopes (saved by Poseidon and shifted to Atlantis before Apollo kills them) on order of Poseidon for Percy after he was born. It is made from celestial bronze, imperial gold, Atlantean steel, Olympian silver, adamantine and a very small part of stygian iron, which allows it to kill mortals as well as monsters. Other than a weapon it can also be used as a medium by Percy to channel his powers.
It has three forms, a sword, a trident, and a bracelet as disguise. It has a unique power that it constantly absorbs Percy's extra energy which leads to decreasing his scent that monsters use to track him while becoming stronger itself.
Maybe due to a mistake and the stygian iron inside it, which turned out to be a blessing, in casting the enchantments to absorb Percy's energy, it also gained the ability to absorbs the energy of any being slayed by this weapon, delaying there respawning in Tartarus while having no effect on mortals unless you want it to, while nothing major in case of monsters but if Percy delivers the final blow to god's, titans and giants with this weapon, it will start absorbing their power, while small (according to gods) but enough to recharge or even overcharge Percy. It may turn as strong as the weapons of the big 3 or stronger in time if enough of them are killed.
It returns to him like Thor's hammer when summoned while having the ability to avoid allies and collateral damage in its path if Percy wills it to. With time it has turned almost into a weapon for god that is being wielded by a demigod. No one other than Percy can weird it.
Fissure Maker -
Percy's secondary weapon that can change into any weapon be it blade or blunt. From spears and scythes to swords and Daggers to war hammers and staffs, anything. It is a powerful weapon and can be used to channel divine powers as well. It is Percy's preferred weapon during duals and practice since the Storm Raiser is too strong that it may harm others unintentionally.
Armour -
Designed by Athena and forged by Hephaestus, it is a master work. It is built to provide maximum protection from both physical, magical, and divine attacks, without hindering its wearer's speed or flexibility.
The gauntlet of armour has claws like Wolverine's claws in both hands that can be used to surprise opponent if Percy is unarmed. The claws are made from the claws of Echidna, the mother of monsters and wife of Typhon. He also has many throwing knives that are made from different monsters' teeth, body parts (in case of monsters like espouse), or spoils of war, that are holstered around his belt, shoulders, and bandolier. Only Percy can remove these knives and no one else. They return after a minute of throwing them. They are a part of his armour so disappear and reappear with his armour.
It is helm is made such that along with providing protection without hindering Percy's vision, it also defends him from mental manipulation-like effects of mist or aura of Ares or his sons Phobos and Deimos. Other than that, it also gives him a commander's aura, making others follow his orders more easily and questioning him less. The armour strengthens its durability when in or near water. It is self-repairing, so unless it is destroyed so much that only atoms remain, it will repair itself in some time.
It is stored in the form of a silver chain with Poseidon and Hestia's symbol and spreads over his body like Iron Man's nano tech suit but the armour resembles normal Greek armour without the skirt. Even covers his legs in shin guard and metal boots
Shield -
A circular Greek shield made by Hephaestus. It has real Medusa's head in it like Athena's shield, that can scare monsters when eyes are closed and turn them to stone statues when eyes are open. It is made to emulate Black Panther's suit's kinetic absorption making it absorb kinetic and divine energies, on Percy's request, to be released when Percy wills it. Because of this ability the shield is almost unbreakable unless it is super charged with too much energy without releasing it. It also has quite a sharp edge and can be used for attack like Captain America's shield and has a hidden blade in it. It can also return to its owner like Thor's hammer or directly in his arms in its disguise. It has a disguise of a Rolex watch. In its watch form its dial has a sharp imperial gold wire that can be used to cut rope that is binding you or to kill someone.
Various Knives and Daggers -
Gifted to Percy by Hestia and Poseidon, there are various types of knives in the collection, from dirks and military knives to butterfly and throwing knives. They also have fire, electric and freezing powers and some can be used to channel elemental powers to some extent. They are kept in his backpack and can appear in his grasp when he wills it.
Guns -
Various kinds of guns from handguns, rifles and SMG, sniper to many more used for long range. Fires Celestial Bronze, Imperial Gold and Silver bullets that never runs out. No hidden form. They are carried in the backpack mentioned below.
A Travel Backpack -
Gifted to Percy by Hestia as he is her first champion, so he is pampered a lot by her. It is enchanted to be much bigger on the inside and weigh only one kilogram regardless of whatever you put inside it. Also, it can shrink to fit in your pocket. In addition, it is also fireproof and water proof and has anti thievery enchantment and a retrieval enchantment like your band. So, you cannot lose it. It comes with separate pockets for money, food, medical kits, clothes, weapons, camping gear etc. It can store anything and everything in optimal condition and anything inside it would never spoil like a personal inventory.
It has an armoury function which summons any weapon or equipment Percy wants from its armoury pocket directly in his hands without having to retrieve them manually in mid fight
A Tent -
Just like the tents of Hunters of Artemis it is expanded on the inside and have a room for everything. It can be shrunk down to a cube and you only must place it on ground to make it. It can also provide you with whatever you want to eat. Cancels outside sound when you want and has a shield to protect and warm you of monster's attack. Given by Hestia.
Chariot/Car -
A chariot gifted to him by gods after he rescued Artemis. It can travel anywhere, be it land, air, above or underwater. It has many weapon systems installed in it, from guns to missiles for different scenarios like tanks or ships or fighter jets and other things, both for monsters and humans, and an AI to manage this system. All the weapons used are replenished from Hephaestus storage on their own so Percy have an infinite supply of them. The AI can also detect monsters by their energy signature and friends if their energy signature is stored in its database. Has a very strong armour as well, along with energy shields. It can run at Mach 2 at its highest speed in air, 500 miles per hour on land, 300 knots above water, and 100 knots underwater. In its car mode it looks like a stylish blue coloured Maserati Spyder. It could also shrink into a keychain or pen drive so you can carry it anywhere.
Hotel Lotus and Casino Card -
Taken during his first quest, Percy used it to build himself a fortune by investing in various shares, storing a lot of money in his mother's bank account, buying a decent house in a nice area. With the card Percy has literally all the wealth in the world as the card has infinite money.
Other than these things, he has a lighter/ electric torch which never ran out of fire or battery, an uncuttable rope, a pocket knife made of steel, a demigod first aid kit, a magical compass which could even point to the direction of the location one wanted to go apart from showing the general direction, a map which can show the map of any place and finally and a canteen with unlimited water. All of these are kept in his backpack.