Here are things I would add to a new trailer without thinking about it again if it was my first purchase and some things you can transfer over to the next unit.
MaxAir II vent covers. Allows you to leave the ceiling vents open in the rain
Or spend a bit more and get a better fan unit installed with a rain proof cover. The multi speed reversible are nice to haves. If someone in your party is short of stature you can have a switch installed down buy the light switch to turn the fan on. Some fans auto open the lid.
If the unit has a slide have the dealer add a slide cover keeps the pine needles, leaves, twigs and dirt out of the top slide seal and helps prevent a leak.
Get them to give you some sort of discount on supplies in their store or visit Walmart and pickup the supplies there.
Yes Walmart actually carries a bunch of RV supplies
They have the Rhino brand hose in a kit and buy a rhino extension right away as well. They are a good hose if you take care of them and come with end caps.
Get a clear elbow for the sewer hose as well. If the RV unit does not have a black tank flush buy the elbow with the flush attachment. Valterra makes a good one. Or have the dealer install a black tank flush for you.
Get a decent brand White fresh water hose
Water pressure regulator
30 amp extension cord.
You will want a 30 amp to 15 amp plug adapter
A 30 to 20 amp adapter is handy and so is a 30 to 50 amp
2 boxes of the lego block ramps
Electric Tongue Jack is something to make your life easier on a hot humid day.
Ditto on the better bed
Some trailers now are selling a foam mattress which is way better to sleep on than the innerspring lightweight they normally put in the trailer.
We started with a trailer with a 6 cubic foot fridge freezer and we brought a cooler
New trailer has an 8 cubic foot and we find we do not need the cooler now
Push handle on the screen door is a nice add on.
If the screen and door are made by Lippert then look for the button in the slide to open the screen latch. Another nice to have. Unfortunately the Dexter doors screen slide is a different size. Still figuring out how to DIY a button like the Lippert
TV: 2013 F150 FX4 Screw Ecoboosted! Luxury trim
OLD TT: 2012 JayFlight 22FB SOLD
New TT: 2014 Jayflight 26RLS