what i would do is pack a nicely sealed bag of chicken feed and of course water and just let them eat and drink when you stop for gas or to eat and drink your self and then dump it out
we made the trek to see my moms grandma ALLLL the way in Oregon gorgeous place but we Texans aren't 😆 used to having our gas pumped for us also we went through Utah vegas Idaho it was quite the trip and also if you are gonna be on the border if I'm not mistaken you might have to watch out for...