Here's the breakdown:
* "Everything": Implies a vast and comprehensive collection.
* "Kitchen sink": A common household item, usually not considered essential for travel or other activities.
* "But": Indicates that the kitchen sink, though seemingly unrelated, is included in the list.
This idiom suggests that someone is being excessive or overdoing it by bringing or including absolutely everything, even things that are completely unnecessary.
Example:
"She packed everything but the kitchen sink for her weekend trip – five outfits, three books, a hairdryer, and even her favorite pillow!"