These bags only hold items related to Inscription supplies, but are larger than the average general bag.
“Pack of Endless PocketsItem Level 75Disenchants into: Not disenchantableBinds when equipped32...Pack of Endless Pockets
“The Scribe's Satchel is an inscription bag that will only hold items needed for inscription...Scribe's Satchel
“This item is created with Leatherworking (510): [Pattern: Royal Scribe's Satchel]. Patch changes...Royal Scribe's Satchel