A three hour journey with cat

We will be collecting our new cat in early January from Essex.  We will be facing a three hour car journey with a hopefully relaxed cat who will simply want to sleep.  Mira is used to going to the vets and has had four litters of kittens and been well looked after.  She is even tempered.

We will buy a good cat carrier.  We'll drop the back seat to make the surface level and have her right next to us (the car is a mini) and secure it.  We'll talk to her/have the radio on.  We'll make sure she has water and the odd little treat.

Any tips for surviving such a long journey with a marginally sane cat/humans?