When you've written and rewritten and settled on just the right item to make the magic flow the way you feel it needs to go, you have to feel confident that you've made the right choices in providing proper expressions of characterization for the characters. There's a tradition to magic rings, for example, that connects them to the soul of the wearer. So, from Gyges in ancient Greece, the rings of power that rocked the realms of Middle Earth or the power rings of the Green Lantern Corps, the choice of jewelry was significant. Middle Earth might not have been so shaken by a Feather Boa of Doom and it certainly would've made the various characters ask themselves some serious questions about their ability to master it.
|"Bow before the...queen!"|
Gyges sporting earrings of invisibility wouldn't work to convey the right feel to readers any more than Hal Jordan flying off in a tennis bracelet and Prada shoulder bag to confront cosmic menaces. Granted, for superheroing, it makes about as much sense as the pairing of a ring and lantern (the two being bitter enemies under natural circumstances), but using that ring to create expressions of the hero's will with which to fight evil was an inspired choice. That was an idea that came over time. Originally, Green Lantern's power was just expressed with lots of eerie emerald light...and a smashing purple cape.
Luke Skywalker and Darth Vader needed swords. Jedi and Sith doing battle with rings simply wouldn't feel right either. Even though rings speak to the expression of the characters' essence, they already had a power for that. They needed the contrast of the plasma sword's martial elegance against the use of the Force or else we'd have been watching a lot of stern looks and hand waving.
A character's accessories are important extensions of them whether distinctive clothing or a unique weapon. Warriors should be matched with swift, decisive means of delivering their awesome might (Thor, Conan, Clint Eastwood). Thinkers should have versatile resources through which they can exercise their cleverness (Bond, Batman, Felix the Cat). Passive folk should find themselves with items that are likewise vague and of limited use. Magic slippers come to mind and they are even more passive than magic rings and certainly out of place in a contest of wills and struggles for one's soul. Dorothy Gale did seem awfully light on her feet, though, and maybe Frodo (they're magic, of course they'd fit) could've handled all his walking better with magic shoes instead of that soul-crushing ring. Maybe we could've even gotten in another couple of song and dance numbers.