Water regulator to control water pressure - too many variances at the various parks.
Progressive surge protector to connect power lead into before hooking up to park's power - very important for preventing unwanted surges and frying some important internal items like microwave, fridge, TV, computer, etc. Water filter system highly recommended and in some cases a water softener system.
Extra water hoses and connectors, minor hand tools, extra fuses for fuse box, extra sewer hose and proper sewer hose connectors, recommended to have a back flush connector for the sewer hose, Oxygenics shower head
http://www.campingworld.com/shopping/product/oxygenics-body-spa-rv-showerheads/5006. Look through the Camping World website and you will get the idea. Understand that you may not be able to buy all the basics at once. Take your time and see what works for you.
Some folks carry a compact air compressor to have a ready source for maintaining proper tire pressure on truck and trailer - very important to keep this checked prior to each trip. Tire pressure Monitoring System like Pressure Pro
http://www.pressureprosystem.com/ has saved many of us from unwanted damage to the RV caused by tire blowout or quick drops in tire pressure due to nail puncture or whatever.
Folding chairs, small outdoor folding table, Weber BabyQ grill (or your choice). Just think about the things that will make outdoor sitting fun and comfortable. Lots of resolutions to the world's problems conducted during the evening pow-wows around a campfire or grill!!
You will also need some type of sewer treatment product to put in the commode after each dump of the black tank to keep down on inside sewer odors. Special toilet paper. We like to use Angel Soft which indicates on the package that it is septic tank safe. If in doubt, place a piece of the toilet paper in a glass of water. Let it sit a minute or two, then stir the contents. If the paper shreds easily and almost looks like it is disintegrating, then it is safe to use.
Coffee maker, crockpot, your choice of eating utensils (many use plastic forks and spoons purchased at Sam's or Costco), paper plates and bowls and plastic cups. Of course, if you are into washing dishes, you can carry Corelle and silverware for the special occasions. You might want to get a roll or two of the rubber grip, non-slip, shelf liner which can be cut to desire lengths to use in wrapping any glassware or placing between plates, cups, etc.
A ladder appropriate to your RV's height that will enable you to properly check slide tops for unwanted debris prior to retracting slides. You will periodically need to check the roof for possible tears, etc. depending on how much you park under trees.
Will you have a satellite system for your TVs or will you depend on park cable? Do you have an air card to use with your computer for internet access?
Others will jump in with their individual recommendations. We hope you have a wonderful camping experience for many years to come. Be sure you take your time on the PDI, take videos if possible to remember how to operate the various controls and valves for the different tanks, how to winterize and un-winterize should you need to do so. There are other threads on this forum that fully explain what you need to know for the PDI.
CJ