No problem. I have brought a foldable litter box from Sturdi [1, 2] with litter in a ziploc. The cats didn't use it. Yes they cried but a carrier that lets you pet them is a way to help with this. I sometimes took them out of the carrier and got away with it most of the time, but one time got told they had to go back in. YMMV

In any case, them being on the seats (in carrier) rather than under them, helped a ton. The cats aren't as freaked out.

[1] https://sturdiproducts.com/products/folding-water-tight-boxe...

[2] https://sturdiproducts.com/products/folding-water-tight-boxe...