Welcome and congrats Rossgn.
things to pack will vary depending on what type of camping you will be doing and with how many.
Will you have full hook ups?
If so, you will want at least 15' of a good sewer hose, I reccommend the RHINOFLEX. An extra 10' extention is nice to have in case you happen to get a site where the sewer pipe is too far from your dump valve hookup on your trailer. This is especially common on longer trailers that have their hook near on end or the other.
25'-50' of water hose is always good. Get a good quality white hose that will stand up to water pressure and it can be used for filling your water tank or city hookup.
A good heavy gauge extention cord for whatever amp your trailer is (50 or 30) and "dogbone" adapters for take it to other plug types than it's norm are handy when you end up with a site that doesn't have the same as your trailer.
One of the first things I did when we got ours was take a measuring tape and measure the door hatches for the storage compartments and the interior dimensions of the storage area. I then went to the local walmart and bought some Sterlight clear storage containers that would fit through the hatches and fit side by side, maximizing the front storage area. I use these for storing the above along with my patio lights. One electric with extention cords, adapters, speare light bulbs, etc. One Plumbing with hoses, pressure regulator, water filter, etc. One Patio Lights, hooks to attach them to the awning, solar lights, etc. Keeps me very organized and easy to find what I need by topic.
Again, Welcome and congrats and don't be afraid to ask if you have questions!