Accessories are things that are unique to the character. Zir magic sword Wellspring, zir steam-powered carriage, a beloved telepathic dog or an unbreakable lasso. These should be items that are important to the character's legend. No one cares what Elric's belt was called, but everyone who's read the stories knows what his sword was named. Accessories should be things that a character has investment in, and the GM should respect that - accessories shouldn't be destroyed or taken away without both the consent of the player (even if it's just “trust me, I'm going somewhere with this…”) and a balancing shift to make up for the loss. It makes a lousy story if Arthur loses Excalibur while taking a bath, unless there's a story tied up in the how and why, and how he gets it back.

Accessories are important because they do a lot of help establish the flavour and uniqueness of the character. In an Amber game, all the PCs might have Pattern, but only one of you has a shape-shifting horse who can speak Spanish.