You will need.
.... sewer hose to empty into dump station or "honey tank", You don't need the most expensive but do not go with the lowest end.
......white fresh water hose, we carry 75'
......electrical cord 30amp, we carry 150'
......wood planks for levelling, you can also buy a variety of products for levelling but we have a variety of 2x10 planks cut up.
......tool kit, look around your trailer and see what is obvious, screw drivers, sockets etc. along with extra pins for hitch and sway bars, fuses, light bulbs for running lights
......we take 18V cordless drill for putting up the levelling jacks, remember the socket also. We also take a 4ft level, makes it easier for levelling.
I could mention many things..LOL