Accessories are things that are unique to the character. These should be items that are important to the character's legend. No one cares what Jayne's belt was called, but everyone who's a fan of the show knows what his gun was named (Vera). 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.
Multiple characters can have points in their ship, the more points spent the more of a connection they have to it. The person who puts the most points into the ship may not be the captain; they are just the person most connected to it.