A few tips - first, create a travel packet for the cat - a copy of the shot records, use the receipt from the vet, it will have all of that. Microchipped? Make sure the chip company has all of your current contact date. Include chip number in your packet. Have good ID photos of your cat, and a photo of you with the cat. Nothing better to prove that the particular animal belongs to you. Put all of that documentation together in a zip lock bag for the cat's GO Kit (I think of it as a diaper bag for the pets). Have a collar with your travel contact info on it, your cell phone number or your destination number. Put a harness on the cat. Probably won't like it, but oh well, better safe than lost. With that harness you can leash. So now the prep is done. For carrier, a small firm sided litter box will do. Firm, not an aluminum sides fall over when stepped on. I like cake pans, Dollar Tree type. Litter, be sure to use usual brand, cats are fussy, and as little as one cup will do in the travel situation, two cups max, avoids kick out. Take small plastic bags for emptying litter at rest stops. At rest stop, if checking on cat, the litter and water, keep car door closed until cat is secured with leash, or the cat is safely tucked away iin crate - they are quick. Food unnecessary for day trip, always have water. Bedding recommended, either the cat's usual nap pad or even a t-shirt of yours with your scent on it (so that means unwashed). Is comforting for the cat. Strongly recommend a misting pheromone products for cats. They work to reduce anxiety, found at most pet stores, fairly low cost, natural product, and does not involve getting the cat to ingest anything. Feliway is one brand.
I have spent hundreds of days as a volunteer with animals affected by disasters and these are basic guidelines. PM me for more. You can have a safe and successful trip with your cat.