We carry a few travel johns (something like that) in the car which are small portable things you can, in an emergency, use for a pee, having had a couple of really awful times stuck in queues on the motorway, absolutely desperate.
That was my first thought re cat litter, hadn’t got round to the actual logistics………
//I just take a flask of coffee, a bar of chocolate and biscuits is a lighter option, small camping shovel, some cat lit and old hessian sacks, not forgetting tow rope, jump leads, warm blanket, change of shoes, gloves, thermal hat and torch.//
That's all right if you're just popping down to Tesco's. But what do you do if you're going on a long trip, choux? :-)