Welcome!
The obligatory question - what are you towing it with???? Hopefully you have a good hitch setup and the dealer shows you how to use it.
You'll need some type of wheel chocks and leveling blocks. Some campers buy the "X"-chocks and plastic leveling blocks, others use pieces of 2X6 or 2X8 lumber. I use a 2' carpenters level when setting up.
A 15A to 30A adapter for the power cord can come in handy. I use mine to charge the batteries between trips, run the A/C when packing, and starting the 'fridge to cool down a day or 2 ahead of a trip.
Get a pressure regulator for your water hose. Most people end up with a Watts instead of the cheap in-line ones.
+1 for a door mat. DW bought a very heavy bristle type and it really stops a lot of dirt from getting in the trailer.
Folks like electric tongue jacks but I'd rather spend that money on campground fees.
If you plan on "dry" camping off the grid, well, that's a whole 'nother subject....