I portioned out a veggie lasagna for DS; I cut it up, wrapped it in freezer paper, then placed in a freezer ziploc bag. I traveled 6 1/2 hours with a full cooler and everything was still frozen solid. Just make sure the cooler is packed to capacity and as CM said, that everything fits together tightly.
And - if something is just slightly defrosted, it is still safe to go back into the freezer. It might alter the texture slightly, but it is still safe to cook and eat.
We'll be going up in a couple of weeks, and I'll be cooking up a storm in preparation. Can't wait to see my boy.