I would ask the dealer what accessories they will throw in to complete the deal.
A power cord (usually 30 amp unless your rig is 50 amp) is/should be included with the unit. Almost everything else is an add on.
Even for the first run, you'll need:
*Water Hose --drinking water grade.
*Leveling blocks and blocks for the jack and stabilizers. These could be simply cut lengths of 2x6 wood, or you could spring for the plastic "lego" pads.
*Chocks for your wheels.
*Sewer hose and connections -- number of hoses needed depends on your black/gray tank set up. Suggest a couple of clear elbows.
*Separate garden hose to connect to the black tank flush if your unit has one.
*Surge protector.
*Water pressure regulator
That'll get you started -- additional things you'll find out depending on your preferences, lifestyle, and where and how you'll be camping.
Good Luck!