Fact
The returning Cozy Sleeping Bag item (from Season of Discovery) grants a 3% XP buff after sitting in it for 3 minutes, and this 3% stacks additively with Cooking's 5% kill-XP food buff for a combined 8% bonus - a stacking behavior PC Gamer notes 'WoW Classic purists would lose their minds at.'
Confidence note
Confirmed (PC Gamer investigative piece, corroborated by name-check across multiple secondary sites)