Welcome, Your Rockwood is similar to our Wildwood for size and weight. To be honest, the starter kit if provided isn't worth much in most cases. First think about utilities. Water, you will need a 25' fresh water (white) hose. Sewer, you will need a Sewer dump hose with the connections. We found the Rino to be good for us. And, a 25' "dirty" hose for washing down the dump hose and fittings. Do NOT use the fresh water hose for this. Power, the dealer should provide a 30 amp power cord to connect to the TT. You will also want to get a "dog bone" adaptor that will convert the 30a male end to a 15a standard male plug for plugging in to house power. A 50' 10 ga extension cord is a good idea too.
Really important for us was a weight distribution hitch with anti-sway. Can't say enough for using a really good WDH. Also at least a pair of GOOD wheel chocks and some form of trailer leveling device. After that go through the kitchen, bathroom and bedroom in the house and make a list of the things you use all the time. It really makes camping a lot easier if those things are duplicated and in the TT ready to go without having to migrate them back and forth. Camp chairs, cause you'll be spending a lot of time outside the TT. Shovel, axe, the usual outside camping stuff, (you can leave the tent home now).
Tools, make up a reasonable tool box. There will be things to fix.
If you happen to go into a Camping World store don't forget the "Buckzooka" You'll need it!.
There is more stuff in one of those places than the Koch brothers could even buy. The good new is other than the WDH, most of the stuff mentioned above is available through Walmart at somewhat more reasonable prices. More good news, how to use and advice on brands for all the above are all over this site. These are some real experienced folks here and most everything has been covered thoroughly in previous threads.
Above all be prepared for a severe case of "Perma-grin" you'll love it!
FR Wildwood 22 RKS
2007 1/2 Dodge 2500, Cummins 6.7
Retirement training completed
Currently enjoying second childhood