A Surge Guard (A good one is over 200 MSRP) is actually cheap insurance I like hard wired for assorted reasons including security and the "Oh it is just one night"
Hughes Autoformer can be helpful in many parks
Water filters are handy too. I made my own el-cheapo and it worked rather well. I used either a Brita or PUR filter pitcher for drinking water.
You will likely like a better (and longer) sewer hose and perhaps water (fresh potable) as well.
Extension cord matching RIG's needs (30 or 50) and adapters to everything Rig to all other sizes including 15/20 amp (standard house outlet).
Three light outlet tester
Voltmeter
Box of assorted fuses
You may find the need to lock cabinets and drawers Assorted methods ask if you find the need and I'll describe some
If you like campfires
Axe, Sledge Wedges both flat edged and pointed (That pointed one was amazing)
Outdoor lighting.