First camper of any sort? If so,
Tongue battery if the deal didn't include it. Group27 deep cycle for beginners.
Potable water hose.
Chocks and wood blocks for leveling side to side.(leave fancier stuff for later)
Small carpenter's level. Place on floor inside door. Side-side first, then front to back.
30 to 15 AC adapter to power and charge at home (but not the AC)
5 gallon pail for grey water (also handy for holding blocks and chocks on road)
Dollar store stuff for permanent fitout: utensils, plates, cups, dishpans, dishrack, clothes line, etc.