Hi Robert and Susan,
Welcome to the Forum! You are going to love your Itasca, they are lovely RVs!
Just in case you did not get this info, here we go.
In line water filter, in line water pressure regulator valve, and a Y connector for you city fill white hose. All can be bought at Walmart and or Home Depot for the Y connector.
CG's ( campgrounds) can have high water pressure and not so clean water lines. Just keeps you from having any issues.
WH (water heater). When not using your RV for a week or more you need to drain the water out or it can get really smelly. Should be info in your manuals on how to do this. If not, have the dealership show you how.
Considering your are in S CA, you might want to think about getting window coverings to keep the sun from heating up the inside. They vary greatly in cost but here are a couple websites.
There are also Magna Shades that you can look up. Shades of these types can cut the heat in your rig by 10 degrees or more, protect the inside from UV damage, and allow you to see out without people seeing in. Allows you a great view out your window without others seeing in.
Good luck, Lynne