We booked Ryanair flights only with Olympic, and got an email regarding the online check in
"This must be done between 7 days and 2 hours prior to the departure of your outbound flight AND also between 7 days and 2 hours prior to the departure of your return flight. If however you purchase allocated seating, you can check-in online up to 30 days prior to the departure of your outbound flight AND also 30 days prior to the departure of your return flight. "
If you don't pay for the above, how are you meant to check in whilst on holiday,and print boarding passes etc ?