As you said, you definitely want to have the printed confirmations with you and don't rely on email on your phone unless you can access it without wifi/cell. I was not able to pull up the confirmations on my phone for my daughter and her friend, even with the ship's wifi, when we had an issue and had to get our printed copies from our cabin to resolve our issues. Unfortunately, all the issues did not show up for us all at once, so we were at Guest services multiple times the first 2 days. It turned out that they didn't have any of their Free at Sea or their pre-paid gratuities entered on their accounts and they hadn't noticed online.