First off, welcome to the forum! And, yeah, the walkthroughs are fast and not all that great for long term knowledge of your RV and systems. Most of us learn from each other, an via trial and error.
Important stuff ... in my mind, the most important things to make sure you have pertain to working with and on the RV. If you have a flat and need to change a tire, how will you do it? I have had 2 different trailers and neither cam with the basic jack/wrench. To me, that's important. I'd hate to waste a lot of time waiting for a service truck ....
Some Campgrounds are really built well and everything you need is close together and close to where you need it .... sometimes, though everything can be a challenge to hook up. Carry an extra water hose
make sure you have an extra sewer hose. Heavy Duty Extension Cord (I would recommend at least 25 foot #12AWG) Gorilla tape. Voltage adapters 20 to 30A Adapter I use often. I also carry a 50 to 30A adapter, used it twice in five years. A small tool kit, especially a screwdriver and pliers or adjustable wrench. There is always some little thing that gets loose ....
Water connection doo dads tend to be important. You will probably want a filter, definitely a pressure regulator.
May want a 90 degree adapter. Everyone sets up differently, you will find the system you like. I carry a lot more than this little list, these items I find myself needing often.