I'd also pick up:
- something to tie down the awning. I use a couple of ratcheting tie downs with a bright colored straps so you can see them better at night and a screw type peg.
- RV-specific toilet paper
- water heater rinsing wand
For the trailer coupler I use something like this to lock the coupler and to hold up the electrical connection cable and the breakaway switch wire.
I'm like the others here who use 2x12s for under the low side wheels. I have one long enough to sit the 2 wheels on and a 2nd, 2 to 3 feet longer, to go under the first and ramp the wheels up onto the shorter one if I need the extra height.
I also have a couple stacks of cut up 2x12s screwed together for use under the stabilizers. I need them anyway to level the Roo in my driveway so they come camping with us just in case they're needed. I also have one bag of Lynx Levelers. I haven't needed more than that so far.