If somebody overpacked for a trip, including many unnecessary items — like an electric curling iron and high-heeled fashion boots for a back-country camping trip — you might say they packed everything but the kitchen sink.
Usually, the idiom everything but the kitchen sink is mildly mocking, because it implies that a lot of the stuff included is almost as absurd as taking the kitchen sink along on a trip. But sometimes it can be used in a positive way, to express the inclusion of everything you could possibly find useful. For example, a car manufacturer advertising a certain car might describe its trunk as being "so spacious that it will carry everything but the kitchen sink."