I'm probably over-thinking this, my brain has been warped by 40+ years of TV news stories on how to prepare for trips to the high country (especially in winter).
Ever since my teenage years, I have always worn tennis shoes if I was in a car/Jeep and not driving; hiking boots otherwise.
As an adult, my what-if mind makes me think of possibly needing to spend the night in the truck on the top of a mountain for some reason, which can become quite chilly overnight. Don't expect your cellphone to work up there.
Drinking water would be good to have, some people get altitude sickness if they exert themselves too hard. A first aid kit in case you fall or otherwise injure yourself, but I think you've already got that accounted for (I seem to remember discussion & pictures on this topic some time ago). A way to start a fire. A hiking stick if you plan to be out & about might be helpful.
When are you expecting to arrive up there? I'm mostly interested in how many people you encounter, the population of the state has more than doubled since I moved here in 1978, and it's really difficult to get away from people these days....