If you have any problems with the necessary information, just fill in default information (examples below.) You can go back and edit when you have the correct information, up until 3 days before your cruise.
Passport numbers/expiration dates. If you don't have them, just put that you're using birth certificates (if that's allowable on your particular cruise.)
Travel information. If you don't have your flights, or hotel reservations pre/post cruise, just put that you're driving and going directly home afterward.
Credit card number. Or you can put that you're paying with cash. When I did an on-line check-in awhile ago, our credit card was due to expire before the cruise, so
DCL wouldn't accept it. So I waited til we received the new cards to complete our online check-in, and ended up with a crummy port arrival time (PAT). I should have just listed that we were paying with cash, got a better PAT, and edited our online check-information later.
Full names (must match names on passports) birth dates, home addresses, emergency contact of friend/family member who's not traveling with you.