Congrats on the RV !
We bought our first one about 3.5 years ago and still find thing we "need".
I'm sure you know the basics but the first things I bought
Wheel chalks , sewer hose , fresh water hose , water pressure reg. , 30 amp to 15 amp plug and outdoor mat .
Things bought after first trip learning the hard way
RUBBER GLOVES
Long lighters
30 amp to 50 amp plug
I have just installed a new flat screen on swing out mount , baby rail over top bunk , collapsible trash bag holder , removable counter top over stove and my favorite electric jack.