Welcome to the forum. You will find you can get lots of advice here. And, as you will see soon, we love to spend your money.
I see you are from Lansing - "see ya" up there this summer...
This is my advice.....
There are some things that some of us consider a necessity. There are some things some of us consider necessary but are really a personal choice.
So...., considering accessories you
WILL need....
2 25' water hoses
1 15' sewer hose
1 10' sewer hose extension
2 25' coax cables (if you watch TV using the campgrounds connections)
The there are
HIGHLY RECOMMENDED items:
An EMS to protect the power going into your camper
A set of pads for your levelers to sit on (especially for non paved surfaces); SNAP PADs are a good choice.
Optional stuff....
A 30 or 50 amp power cord extension (I prefer a 30 amp even tho I have a 50 amp camper; it is easier to coil up and carry and isn't used often)
Leveling blocks
I may have missed something but I think those are the basic necessities.
Then there is an endless list of other "stuff" like charts, mats, grills, etc. My suggestion is that you use what you have already and find out what you really want. I see lots of folks who immediately run out and buy chairs, table, grills, mats, etc. You can spot those new folks pretty easily at campgrounds. But then they find out they like some other chair or grill or whatever more, so they buy a second. We've all benn through it.
Good luck, safe travels and happy camping.