Put the car seat in seat so that you can get in the back easily. Don't be like me on our first trip w baby in the middle, climbing over the seats and diving into the back seat only to find there was barely any room and my seat belt had to go under car seat to attach.
Have bottles ready so that you can feed baby wo stopping. I know at that age bf could take 45 min, I had pumped a bunch in advance for bottles so that we weren't sitting on the side of the road while I was nursing.
Have mobile diaper station ready to go and in easy reach. A receiving blanket covering back seat, diapers and wipes are all you need. Plastic grocery bags are good to contain any grossness until you can get rid of it.
Also the receiving blanket can be used as a sun cover in a rolled up window if you need it.