We drove with cats from California to Calgary and because of car trouble it took 5 days. So almost a week. I had my cats in cat carriers always during the car ride. I used good sized carriers so they could move around a bit. I didn't give them food or water during the daily driving. I was trying to avoid them needing to go to bathroom during the drive. At night in the hotels we let them out of their carriers and fed/water them. I brought a plastic container with a lid at Target to use as a litter box. It was small enough for easy travel but big enough for them to use. So each night it would be in the hotel bathroom and then I would pack up by scooping it and putting the lid back on. Kept the smell at minimum. I am a little OCD so I also used a lint roller to clean up any litter on the hotel floor from the cats.
We only had one urine accident during the drives and besides some meowing the cats did fine. I would recommend don't forget a few extra towels for their carriers just in case.
the box I got was like this one:
http://www.walmart.com/ip/Sterilite-6.2-Quart-Modular-Latch-Box-Bamboo-Grass-6pk/44785779?action=product_interest&action_type=title&item_id=44785779&placement_id=irs-2-m2&strategy=PWVUB&visitor_id&category=&client_guid=a0fba85b-51ad-4a64-992e-9ed68e87a2f6&customer_id_enc&config_id=2&parent_item_id=44785774&parent_anchor_item_id=44785774&guid=99dd447e-4f92-485a-a112-ce4517179434&bucket_id=irsbucketdefault&beacon_version=1.0.1&findingMethod=p13n