Congratulations, and welcome to the website. You'll get a feel for what you want to do to customize and make things easier as you go along. I'd second a few things which have already been mentioned, like a surge protector for your electricals, a decent quality water hose, and a good quality sewer hose setup. Add a visible connector fitting to that sewer hose, so you can see when the water is running clear. Also, you will want a second water hose, because the water you use at a dump station is often reclaimed, and you never want that running through your fresh water hose. Label them with a permanent marker. Don't ask me how I learned that.
I would add that you should have a water pressure regulator. I use a simple camco one made of brass. Just in case you get some water hammer in the campground, you don't want that affecting your piping inside your unit. And long rubber gloves for the sewer dump process, just because you may run into a leak here or there you have to fix quick, when the couplings are not necessarily fitting tight at first. Especially when you're a newb, it can happen. Get a small bubble level you can set on the floor when leveling your unit. And a large Home Depot style 5 gal bucket doesn't hurt for just about a dozen different uses. I used mine to carry the fittings and couplings for the sewer hose, and I'd toss my gloves in there when I was finished. Now, I still use the gloves, but I just toss them into the floor of the sanitary bay on the motorhome.
2006 Jayco Seneca 34SS
2006 Jeep Wrangler Unlimited Rubicon Toad