If you can keep the gamgling to a minimum and choose very wisely on excursions, you should be fine.
When you board, they will ask you for a credit card to put your charges on, then on the last day, you'll receive a detailed list of all the charges and then it will go on the card you gave them. Some people just give them a certain amount of cash and keep track of their purchases onboard, not sure what the amount is to start it.
I think you'll enjoy seeng the towns you stop in, make time to take a walk around, all very friendly and filled with other cruise passengers like yourselves.
Have yourself a wonderful time, take lots of pics...I love cruising on Princess in Alaska, they really know how to do it.