Work backwards from the overnight stop
An overnight journey is really two shorter journeys with a rest between them, and the feeding plan should be built that way. Start from the stop: what time will you arrive, who will be there, and does the stable provide hay and bedding or expect you to bring everything? Then work backwards to loading. A horse who arrives at the stop already thirsty and empty will spend the night catching up instead of resting, so the plan begins with forage and water before you leave home, not at the first services.
Hay: his own, measured and generous
Send the hay he is used to, in the nets he is used to eating from, weighed out or at least portioned for the whole journey plus the stop. Sudden changes of forage mid-journey are a gut risk nobody needs, and strange hay he refuses leaves him empty for hours. Nets for the travelling legs should be filled before loading so nobody is stuffing nets on the ramp, and the overnight ration should err on the generous side — a horse with forage in front of him chews, drinks and settles, while a horse who finishes by midnight stands hungry until morning. Pack a spare net beyond the plan; delays happen, and extra hay is cheap insurance.
Water: carry the taste of home
Horses are fussy drinkers, and water that smells or tastes different is the commonest reason a travelling horse dehydrates. Fill substantial containers from his home supply before departure, enough for the journey out and offered at every pause, and if the stop's water is all he will get overnight, mixing home water with stable water in his bucket softens the change. Some owners flavour the home water slightly for a few days before a trip with something the horse likes, then flavour the strange water the same way; whatever trick you use, practise it at home first, because the middle of a journey is no place to discover he hates it.
At the stop: water first, hay second, checks third
Unloading into the overnight stable, offer water before anything else and let him drink his fill, then walk him briefly so he stretches, passes droppings and sees his surroundings before you put his hay in. Refill the bucket after he has eaten, because horses often drink most once forage is in them, and make sure a full bucket is within reach all night, checked last thing. Note how much he has actually drunk and eaten; those two observations tell you more about how the journey is going than anything else, and a horse who has neither drunk nor eaten needs a changed plan, and a vet's advice, before the second leg rather than after it.
The morning leg
Before reloading, let him empty himself, offer water again, and top up the nets with the same hay. Recheck that containers for the road are full and that buckets left at the stable are clean. Keep the second day's driving broken by water stops just like the first, and resist making up lost time by skipping them: on an overnight journey the stop is not an interruption to the plan, it is the plan.
Because KinsLe Care Pass hands the overnight staff his feeding amounts, water routine and quirks in one clear temporary pass, the horse's carefully worked-out plan is carried out exactly as written, even by people who met him an hour ago.