Great list! I think the only thing I'd add is to make sure there are enough snacks and water for the parents, too. I often was so focused on the baby, I'd forget that *I* would need snacks and water, too (especially when breastfeeding!).
Like you, we also learned the hard way to keep adult clothes in our bag/car, too. My husband had one of our daughters spit up her entire meal on him when she was an infant and we had done a family day trip to explore a nearby city. Unfortunately, while he was able to wash most of the spit-up off in the bathroom, he had to walk around with a wet shirt for the rest of that windy, cold day!