Not much time for writing full magic item entries. But that’s OK. This thread is supposed to be about idea generation, not finished products.
1. A wardrobe closet that carries a spare set of equipment.
Wondrous item, legendary (requires attunement)
This tall, rectangular wooden closet is about the size of the Police Call Box (aka the TARDIS) from Doctor Who. The frame is supported by sturdy iron wheels at each corner that remain perpetually lubricated and rust free.
Three of the wardrobe’s interior walls contains hooks, shelves, hangers and numerous means of storage for clothing, armor, shoes, jewelry, and all manner of objects that may be worn, as well as the ceiling. A full-length mirror backs the entrance to the wardrobe. Facing the mirror is a fully articulated mannequin that changes height and shape to match the proportions of the creature it is attuned to. The interior of the wardrobe is always lit comfortably by magic from an unseen source.
If you are standing outside the wardrobe, and are on the same plane as the wardrobe, you may use an action to teleport all of your worn and held objects to the wardrobe, and replace them with whatever objects are worn and held by the mannequin. The wardrobe can’t be used this way again until the next dawn. When you use this property of the wardrobe, its magic automatically ends all spells effects, other ongoing magical effects, and any other effects active on your person that were caused by your first set of worn and held items
2. Monty’s Haul:
On a successful attack, this magic weapon steals a one of a creature’s three attunement slots and gives that slot to you. You can receive no more than three attunement slots this way. That creature can take back its slot by making a successful melee attack against you. While you have an attunement slot from another creature, you may attune to one extra magic item beyond the normal limit of three (DMG 136).
3. Shield of the Wounded Warrior:
A shield that drinks evocation magic and provides you with hit points.
4. (spell) Ride the Lightening:
Summon the fury of Talos to be struck by lightening and teleported to a random destination within the same region of the storm, or to someplace where the deity determines you are most needed.
5. Gems of Whiplash:
Say the command word and get rocketed back to the location of the last gem in this five gem set, and at an awesome rate of speed. You will hurl. You’ll be yanked into the sky like the unfortunates in the movie “The Forgotten”, except that you get to land somewhere and (hopefully) walk away.
6. Hellwalk Boots:
Active a blazing inferno at your feet with the boots, or jump in a fire on the Prime Material Plane, and then step lively as you race through the Hells for a short while until you find the second fire conjured up by your boots to jump through to make your way back home and to your destination on the Prime. But beware: the denizens of hell love a free meal and a chance to torment, and they always know to toss the boots back through the fire so the next fool and his friends will come, because they’re the ones that made the boots.
7. Ring of Combat Critiquing:
This magical ring “remembers” the last combat you participated in. A combat is as any encounter where you rolled initiative, and the ring records everything from your point of view until the combat ends. Any time before your next combat, you may command the ring to replay the last encounter. The replay consists of a Programmed Illusion that fills up to 30’ space, includes sight and sound, and lasts for no more than 5 minutes. There is no limit to the number of times you may replay your last encounter. The last replay stored in the ring is erased the instant a new combat starts .
8. Shield of the Fire Thief:
Although this surface of this ornate shield is carved to resemble a flattened red dragon’s head, it plays no favorites when it comes to dragon breath weapons. Any time the wielder of this shield is struck by the breath weapon of a dragon, the shield automatically prevents all damage and deleterious effects to the wielder, and it steals the dragon’s ability to use its breath weapon. The dragon’s breath weapon returns at dawn on the day after its breath weapon was stolen. This shield may steal no more than one breath weapon this way.
9. Gauntlets of the Pious Mercenary:
These simple gauntlets provide healing to their wearer. Whenever bearer of the gauntlets provides food and drink to the needy, to the wounded, or to the starving by handing it to them and assisting them to consume it (if necessary), the bearer is healed 8 hp per person fed. For up to one day after feeding others while wearing the gauntlets, if the bearer harms someone they fed, the bearer is then cursed: he or she may not benefit from healing magic of any kind for one year per person harmed, and the gauntlets may not be removed by any power short of a Wish spell or divine intervention.
10. Gauntlets of Extra Hands:
Whenever you require extra help with a physical, non-combat task (such as lifting up a heavy object, carrying a fallen comrade, steadying a ladder from falling, etc.), these Gauntlets create a second set of your hands that may be “set” in place and then commanded to act as you would act while performing the physical task. For any of the tasks listed under Other Strength Checks in the PHB, p.176, these gauntlets confer advantage on your Strength roll. These extra hands disappear when you stop performing the physical task. They may not be used to make attack actions of any kind.