The most important things you can bring with you on your first trip are common sense, patience, and sense of humor
The next two most important items are your manuals and a pen and paper to take notes, write down questions for later research, and to start creating your arrival and departure checklists.
I second Bradnailer's recommendation to camp near civilization your first time out with a new trailer. This is especially important if you are new to camping in general or new to your type of trailer in particular.
I've had a few trailers and I will always spend a night or two camping in the driveway to make sure I understand all of my systems and procedures and then do the first trip nearby just in case I need to run home for some tools or ?