Traveling with a beta?

So I'm adopting my pets tomorrow from someone who's moving and can't take him. He's healthy etc and she lives about thirty-forty minutes away from me. So he will be in the car for that amount of time. She said she will put him in a bag. My question is how do I transport him in the bag? Should I have a plastic container and put the bag in there or should I just have the fish in my lap or what?