what did they do for gas?

Going 40 miles for fuel would not be unusual. A small town like that wound't always have a fuel station, although most out here in the west do indeed have at least one pump. Each of the little towns (much like Perfection) in eastern CA where this was filmed have at least one station/store.
Even though we have gas and a grocery store, in our town, we drive 100 miles one way to shop for clothes, staples, and case lots of food. Many people go for the night, enjoy a meal out, a movie, and do shopping the next day, and head for home. We schedule our gas so there is just enough to make it over the hill, so we can tank up on fuel for up to 30 cents a gallon less.

I don't remember if they have them in this movie, but Perfection had pumps in Tremors 3.

By Grabthar's Hammer...what a savings.