Pay for internet access on the ship or
Have a trusted family member check you in from home or
Wait until you get to the airport to print your boarding passes if you have EBCI.
No worries, with EBCI you do not have to do anything other than show up at the airport on time. The $10 fee covers automatic check you in and assignment of group and boarding number.
Folks who need to check-in 24 hrs will either have to pay the ship internet fee, rely on family/friends at home, or wait until the ship is within cell signal and use their smart phone.