Hi Clsandi and welcome to Cruise Chat.
Usually, Princess asks that you pack a separate, smaller bag for you to use during the land portion of your trip. The coaches and trains don't usually have enough space to stow a big suitcase for everyone. You will get separate luggage tags, too, one to put on the small suitcase you plan to take on the land trip, and one to go on the luggage that will meet you at the cruise ship. That luggage will not be accessible to you while you're on the land trip.