Most cargo ships putting into the port of Everett, Washington, brim with cement and lumber. So when the Olive Bay docked in early November, it was clear this was no ordinary shipment. Below decks was rolled steel bound for Vancouver, British Columbia, and piled on top were 181 containers emblazoned with the Amazon logo. Some were empty and immediately used to shuffle inventory between the company’s warehouses. The rest, according to customs data, were stuffed with laptop sleeves, fire pits, Radio Flyer wagons, Peppa Pig puppets, artificial Christmas trees and dozens of other items shipped in directly from China—products Amazon.com Inc. needs to keep shoppers happy during a holiday season when many retailers are scrambling to keep their shelves full.