I am coming to the conclusion that filling them all up in SLC after leaving Ryan had to do with disposing of the weapons. She didn't need gas in the cans, even if, for the sake of argument, that Winnemucca was the only place to get gas after SLC, she knew she could make it there, it was a shorter trip than Pasadena to Mesa, and she made that with what was in the tank.
But she told Juan that 15 miles outside of Winne. the low gas light came on and she searched on her phone and found the closest station was 15 miles away, so she put gas in the car from a can.
But when she gets to Winne. she puts 12.175 gallons in the car, one transaction only. He uses it to establish how much gas can fit in the tank but also showed that had she put any from a can into the tank it was extremely minimal because she only drove 15 miles and could still fit more than 12 gallons in the tank.
I say that she went from SLC somewhere to dispose of the weapons, used some can gas for burning the clothes and nearly ran out of gas getting back on her route outside of Winnemucca. Otherwise there is no reason on earth to carry a smelly bomb in your trunk in the summertime. In the desert.
Weapons must be west of a point between SLC and Winne., or around the Great Salt Lake - had Travis and she ever made a trip there? If she actually did call a gas station in Winne. the ping could be used to pinpoint which direction she was coming to Winne. from.