I used to travel solo 8+ hours to see a boyfriend at his ranch in a remote area of Montana (no lights visible anywhere, at night; and grizzlies around the ranch house on a regular basis!). I did this 2-3 times a month, for over a year, back in the 1980's.
Montana winters are not to be ignored and I always packed and planned accordingly. Warm clothes and a down sleeping bag, some food (energy bars, bad enough that I would need to be desperate to eat them!), water and energy drinks, a shovel, matches, even kindling and pieces of seasoned firewood. My Dad gave me several flares, just for emergencies, and I carried a couple of lanterns and flashlights (always had fresh batteries and spares, as well).
I did not carry a cell phone (not easily available at the time), but I did carry both a .38 and a .45! Not to put too fine a point on it, I am a crack shot (practiced weekly at a federal law enforcement firing range). I applied for and was issued a concealed weapons permit from my state. Law enforcement friends told me that, though my permit had no bearing in another state, the fact that I had one would always carry in my favor should any trouble occur. I kept one of the guns on the passenger seat, under my purse. The other, I kept under the driver's seat.
I really enjoyed those trips (I missed the trips after I dumped the boyfriend!). It was very freeing and fun! I had music to listen to and could stop when I wanted. I got to know the folks that worked at certain truck stops and mom-&-pop drive-ins. I knew the route and never deviated from it.
That last part is VERY important!! Once you commit to a trip (especially in winter), stick to the planned route and always let someone know your route and plans. Leave a copy of your car description and license plate number (my folks had a photo of my car and of me: full body and close-up).
Of course, the obvious goes: NEVER pick-up ANY hitchhikers!
These days, with GPS & cell phones, I wouldn't hesitate to drive alone again.
On one of my return trips from Montana, I had to wait for several hours when one of the passes closed due to an avalanche. I had 15 smoked hams in my car (yup, 15 hams) which I'd bought at a little hole-in-the-wall ham store (they were famous for their hams, which were quite delicious!). I figured I'd make it until spring, as long as I had a container in which to melt snow to drink! Happily, I was on my way, again, in 6 hours. That did make for a looooooooooooong days drive (though the car smelled heavenly)!
So, simply plan ahead and have fun on your trip!