Going out for the day

My family is going out of town about an hour or so away, my baby is 6 weeks old. I'm exclusively pumping, and my lo eats about 4 Oz every 2 to 3 hours during the day. I have no extra bottles of breast milk in the fridge. It doesn't seem like I produce enough extra milk to store away for days like this. I'm wondering if I should get a container of formula to supplement for the time being? And still pump and feed him breastmilk during the other times? Any suggestions? If so what kind of formula do you all recommend?