FTM feeding on the go.

Hi ladies. I have a formula on the go question. Our girl is 7 weeks old and we usually feed her a mix of pumped breast milk and premade, ready-to-go formula. We also have a few "back up" 2oz formula bottles but they're not her regular kind and I am convinced they don't sit in her as well, plus she often drinks more than 2oz per feeding. Soooo my question: This Saturday we're all invited to a baby shower. Between everything, we're looking at 7-8 hours out of the house. I can bring about 5oz of breast milk, but what about the rest of the feedings? What do I do? (In 7-8 hours, she'll probably drink about 12oz or so in total.)