I haven't hit this point in my son's life yet, but I can remember what my mother used to do for me when I was his age (and older!) to keep me content on long road trips.
In the weeks leading up to the trip, my mom would start secretly accumulating small toys (Yes & No invisible ink books, Mad Libs, wind-up toys, blocks, coloring books, dolls, etc.) that she would then place in a big canvas "goody bag." When I was really young, she would let me pick something out of the bag after I'd been quiet (or at least not disruptive!) for half an hour. After I turned 8 or 9, she'd just give me the bag at the outset of the trip and let me amuse myself with whatever she'd found to put in it. The novelty of so many new toys kept me distracted from the length of the trip, and (at least in the early years) curiosity about what could be in the bag kept me quiet long enough to find out! Nothing in the bag was particularly expensive--even the bag itself--but I'm sure the result was priceless.
You might want to put together a bag for the trip out to Arizona, and have your sister put one together for you to take back with you. Then you don't have to carry a whole bunch of extra stuff on your outbound trip, and whatever she finds will be a surprise for both of you on your way home.
Have a great trip!