I'm sure others will have more to add but I'll mention a few things.
If the dealer does not supply a sewer hose with the trailer, you will need one (Rhinoflex is a very nice hose that comes with adapters for various sewer openings).  Also make sure you get an electric plug adapter to step down from the big RV plug to regular 3 prong 20 amp.  You want a fresh water hose (white is usual color) and a pressure limiter to screw onto it so you can't blow out the trailer's lines with too-high city water pressure.  Get a couple of wheel chocks.  Some short 2×4 or 2×6 pieces for leveling the trailer can be handy.
Inside, it's the usual stuff.  Bedding, plates, cups, flatware, utensils, a pot and a pan (or more), towels, RV toilet paper, soap, etc.  First things I added to my trailer were a towel ring and a paper towel holder.  I want a small mirror before my next trip, too.
How many inches of drop?  I could only guess.  6 or 8 inches or more?  Maybe someone else has thoughts on it.