To get started, you will need the basics. You can decide what else you will need as you use your rig.
The very basics are, a white potable water hose, sewer hose, along with the fittings needed, water pressure regulator, dog bones, these will step a 30 amp shore power up to your 50 amp plug, there are a bunch of different configurations, leveling boards if you don't have an auto leveling system and a level.
Once you get your feet wet one thing I would recommend is some sort of electrical protective device. There a a couple of brands available.
Also a clear fitting attached to your sewer drain will let you see how well you are rinsing your black tank is a nice thing to have.
An assortment of tools along with a multi meter are also good things to have.
And since you are in DE, you will need to winterize soon. Don't forget about that.
And of course your personal items including cook and dinner ware.
This should get you started.
Have fun on your first trip.
Peace
Dave