Taking kitten on 8 hour car ride

I need advice. We just got a new kitten a week ago. She’s 13 weeks old. (We rescued her) so it wasn’t plan. And yes she’s already been to the vet. Anyways, we don’t live in this state. We were only here for a few weeks. We already have one cat with us but she does great on car rides. She actually loves them and usually sleeps the whole way. (We let her out to pee and eat when we stop)

This kitten however, she’s adjusting great with us. Very loveable, cuddly, and hasn’t had any problems at all. But when we put her in her carrier, she meows Nonstop very loudly and scratches. Obviously this is going to be a long trip and I’m worried about her. I’m especially worried that she’s not going to go to the bathroom or eat or drink when we stop. Or worse, she will pee/poop all over herself.

She’s a very needy kitten. I’m currently in the bathroom and she’s outside the door meowing because I left her alone for one minute. I tried to hold her carrier in the car but it didn’t work and obviously it’s not safe to let her roam free in the car. Any advice other than frequent stops?