Suggest you check out the ports of call board on cruise critic to find suggestions of what to do in Panam.
About 450 of us did the ferry trip of the canal from OV in November, it was great and seemed better value than the train. It is a long day, 2 hours in the coach each way. They give you a picnic lunch on board, but I also take something off the breakfast buffett and crisp/ fruit etc although there was plenty of free soft drinks on board. Also ensure you have plenty of sun cream as it was very ho.