I agree with what others have said about starter kits... They are short, both water and sewage hoses and cheap.
Our dealer included all hitches, wiring and sway bars. We also had a hitch installed on the trailer to pull the boat behind. His cost. You may want to ask about tow mirrors, again get the good ones, actually try them on your vehicle before you leave the dealer. We also got free winter storage and prep. And no it all wasn't hidden in the cost, we set the price then added, LOL. We paid 7,000 less than other dealers wanted.
My list....tool kit, look around your trailer and see what you might need for tools, we carry another in the boat. We also carry extra pins for hitches etc., we had one break inside one of the jacks, had extra! .....You can never have too much electrical cord or water hose.....Invest in a "honey tank"....
A mat for under the awning saves a lot of dirt entering. Make sure to spend a bit more and get the one that is safe for grass, no damage. Some parks will not allow anything but that type......I could go on, LOL, I still have my original "for the trailer" lists.