Add booked data directly through Planapple. Using TripIt is annoying. And please support cruises!
You can enter any items you'd like directly into Planapple, using the "Add Item" links at the top of every notebook page. And you can forward your confirmations (or any email) to firstname.lastname@example.org from your confirmed email address to add it to your trip.
But I'm guessing this suggestion is a request for Planapple to automatically "read" the emails and enter the correct items and times into your trip, like TripIt does. The folks at TripIt have invested a lot of time and energy in making that work well, and they're really good at it. So it's probably not something we'll be able to duplicate with Planapple.
(Incidentally, there are some separate suggestions here in the forum to make it easier to schedule an item in the itinerary, and we are planning to improve that.)