If you have your Ship tags on your luggage, you should be able to leave your luggage with the porters and do whatever, as long as porters are accepting luggage. Some of that depends on your check in time or when check in starts for you and/or others. If check in for the cruise does not start until 4:00 in the afternoon, for example, there may not be porters there in the morning. Cabins are usually not ready for you to drop luggage for an hour or two after boarding begins. So, "dropping your luggage on the ship" would probably not be possible. Dropping your luggage with porters might be. If you have a carry on with necessary items, you would need to keep that with you during your "time in port". However, "All aboard" can be a totally different time than when your ship leaves the port. There are all sorts of activities, including muster, that happen, before you set sail. Never, and I mean never, wait until the last minute to board a ship, either in the home port or any port. They may have pulled up the gangway. The ship will not wait for you.