You should get a started kit that includes a white water hose, cheap sewer line and maybe a roll of toilet pater and some liquid chemicals for the black water tank.
My list would include
1. Sewer Hose, two section type (10ft each) with a good 90 degree screw connector into the ground.
Like this HOSE
Also get one of these clear 45 degree bends LIKE THIS
This way you can use your thank flusher and see when all is clean and clear.
2. Toilet paper 2 ply only. Angel Soft Walmart 12 rolls for $5.97
Don't waste your money on the more expensive stuff.
3. Water regulator. You may get on in the free pacjage but not needed right away. LIKE THIS
4. TV cable for campground cable 25ft minimal LIKE THIS
5. Blank tank deoderizer and digester stuff. LIKE THIS
Basic hand tools
I would also make sure you bring a video camera so when you are shown about the rig you can tape it so you can review later.
Make sure to ask lots of questions at that time and if you know someone who has a trailer ask them to come along to make sure they don't BS you.
You should get all propane tanks full
Full gas tank
Make sure all tires are properly filled according to the yellow sticker in the rig wall or in cabinet wall.
If you find anything wrong make sure they document it on your copy with their signature.
Make a followup appt then and bring rig back for them to solve warantee issues. It none it can be cancelled.
If the engine has lots of miles expect a free oil change.Run and use everything 2 or 3 times sucj as drains, faucets, shower, water heater on gas and electric. Oh make sure all chassis batteries are full of water and charged.
Have them plug in AC power and see how things run. Then disconnect and see how they run on batteries.
Test generator with load.
I'm sure others will add to my basic list.