Congratulations on your camper! I would strongly suggest you pick up a rubber mat as someone else mentioned. It will keep the camper from sliding. The spray-in liner (which I also have in my truck too), doesn't give enough grip. Gives a nice cushion layer to the underside of the camper too.
Get a couple of hoses. One for filling your fresh water tank, and a garden hose for other purposes like flushing your black tank if it has that option.
Maybe a water pressure regulator too.
And latex gloves for the dirty work after a trip.