It's only about 75 miles from Ritzville to Pasco, and with basic planning you won't have to stop anywhere in between. Most of 395 between these 2 points is 70 mph freeway through some fairly desolate landscape with very limited services. If you fill your tank in Coeur D'Alene or Spokane, you should have no problem making it to Pasco/Kennewick. As I remember, 395 has continuous cellular coverage, I have AT&T.

The biggest selection of convenient services are in Kennewick after you cross the bridge on 395. You have about a 4 mile stretch of busy city street with every gas station and restaurant known to man.