We'll Go First
Someone on the AIPackList team once packed for a ski trip and realized at the resort that the "gloves" grabbed in a pre-dawn rush were actually a pair of oven mitts. They were, briefly, used as gloves. It did not go well.
The Fails We Hear About Most
A few categories come up again and again once people start comparing packing horror stories. The mismatched-shoe pack, where two different left or right shoes somehow end up in the bag. The full-week-of-clothes-no-underwear pack, usually discovered the first morning of the trip. The "I'll just wear the same jacket the whole flight" plan that falls apart the moment a connecting flight lands somewhere twenty degrees colder. And the classic: a fully charged phone and zero chargers packed, followed by a frantic hotel-lobby search for a compatible cable.