AGGGH! #3: Handling Litter Needs While En Route?

Finally, a logistical problem. I'll be transporting Charlie around
Thanksgiving (assuming he's well) for a semi-extended trip. How do cats
handle litter needs when they are away from home? Specifically, I'm
wondering how he might handle elimination while in the carrier? Are
there litter box solutions that are built for inside carriers? My mom
can set him up with a sort of little personal litter box when he gets to
their house, but I'm wondering how he might handle himself en route.
Estimated travel time in the carrier, each way, is about 5.25 hours.

My thanks in advance to everybody who answers ... this new cat-daddy is
finding himself a l'il overwhelmed at times ...

Mike