If it's less than 3 days prior to embarkation, you have to call since it won't be available online. But I believe you can book up until the day prior. Presumably you'd still get an email confirmation that should get you into the terminal. Luggage tags are available curbside with the porters. You might need to do the rest of the check-in stuff/paperwork at the terminal since you won't have access to online check-in.
Enjoy your cruise!