Only you can decide what you need, and what you can do without. Some people don't use their indoor cooking facilities, some don't use their showers very much, some must have campfires and outdoor stuff, some hate the outdoor stuff and spend more time inside reading.
What you need to have along will depend on how you plan to spend your time. Outdoor activities? Swimming? Cycling? Rock climbing?
Obviously you need the basics: several lengths of drinking water hoses, perhaps an extension cord for shore power, extra gas cans for a generator if you take one, the various adapters for power pedestals, extra water filters if you use them, jacks to lift the trailer if the need arises, various tools depending on your level of expertise, etc.
You need to take a couple week trips to learn what you need and what you just want to take along, and trim the lists as you go.
Oh yeah, the important thing: money. :)