Every cartoon character has their own convenient hyperspace pocket. It's pretty much been a big trope in cartoons since the early 20th century.

I think Sam, along with Raven from Teen Titans, were the two characters of the mid-00s that got me into taking a liking towards goths. Even today I still like to listen to music considered "in" with the goth crowd (The Birthday Massacre, The Cure, various electro-industrial groups that the "cybergoth" subset tends to love, etc), and find dark clothes combined with either dark or pale makeup quite appealing.