We are getting ready to do out 5th B2B. we totally enjoy them. It is really nice if you get to keep the same rooms. You don't need to pack up on the last night of the first cruise. If you have to move rooms, you just pack your suitcases and leave them in the room, the CM's do the rest. I was able to leave my hang up clothes in the closet and they magically appeared in the same closet space in the new rooms.
On the last morning of the first cruise, we get up and around and head to breakfast upstairs. Be sure and eat breakfast on that day because you might starve before you get back on around 10:30, lol. You SHOULD get a letter in your stateroom the night before the first cruise ends. If not, just go to guest services. The letter will tell you where to meet up and what time the next morning. When we get off the ship they place us in a holding area until the ships computers have been updated with the new passengers. You will need to settle your account for the 1st cruise before you leave the ship. Normally we are back on around 1030, be sure to take your passports and key to the world tickets with you to get off the ship.
If you are in the same port (like Port Canaveral) you can take your dirty clothes to the vehicle if you want. We have done that. We actually had clean stuff in the car and just switched out. Just be sure that you don't have the smelling stuff where air can get to it. You COULD come back to an terrible smell that will last for days.
Anyway, when you get back on you have access to your rooms. Be mindful that there are CM's going through the halls cleaning. We do our best to stay out of the way. We usually just stay in the room till noon and go to the upper deck buffet for lunch. As soon as we are done we just go back to the room. We aren't big on swimming onboard. They ask us not to cross the lines to often to get access tom our rooms. especially since folks will actually start sitting on the stairs on the floor where their room is as early as noon. It's not a great thing when we go to cross the line to gain access to our room about 12:30. You can hear people talking about what those people (us) did when we crossed to go to our rooms.
A PRO is that you CAN have the same dining team for the back end of the B2B. Or you can switch, we have done both. One team was not very good so we requested a change. The second team we had was actually my favorite team of the 30
DCL cruises we have taken. Other times, we like the servers so we keep them. It is odd when we show up for dinner the first night and everyone around you changes, except the servers.
The drill on the 2nd cruise is not a big deal unless you make it a big deal. Everything else is pretty much normal. There is usually a movie playing in the theater the afternoon of the first days, so you can go to that movie in the afternoon if you want.
I love the B2B cruises because like others have posted, you get everything twice, shows, dinners, PALO, and CC is some cases. And if you didn't like the experience on the first cruise, you can do something else. And usually by the end of the B2B, especially those 7-night cruises, B2B (14-Nights) you are ready to go home. Not, really but more ready than after just one cruise.