In most cases, you do not need to carry your physical passport when getting off a cruise ship for a day-long shore excursion, provided you are returning to the ship the same day. Most cruise lines utilize a "Ship's ID" or "Key to the World" card, which acts as your primary identification for the local port authorities. When you disembark, the ship’s manifest has already been shared with the local government, and your cruise card is your proof that you are part of that group. However, you are almost always required to carry a government-issued photo ID (like a driver's license) along with your ship's card. There are exceptions: some countries (like Russia or certain parts of Asia) may require a physical passport or a copy. It is a common "best practice" to carry a high-quality color photocopy of your passport's photo page while ashore. This ensures that if you accidentally miss the ship's departure, you have the necessary documentation to visit a local embassy and arrange for alternative travel to the next port or back home.