How Far Can A Horse Travel In One Day Allowing For Food And Rest?

It depends hugely on the animal itself, as well as the amount of effort it has to expend in the going.  Weather conditions, terrain and breed come into it, too.

Take a strong, medium build animal in excellent condition, of medium-tall height with not too heavy a rider or load, going over light to moderately difficult terrain, and it might be able to handle up to 100 miles (with rests, food and water) in a 24 hour period.  Most horses would wear out if they had to do this day after day, though.

On a regular basis, perhaps 4-5 days a week, most well-looked after horses of suitable breeds are capable of travelling 20 miles a day without ill effects.

Anna Sewell's famous novel Black Beauty details the living conditions of horses in England in the late 19th century.  She describes hansom cab horses pulling heavy loads for 15-40 miles a day, six days a week, for months if not years on end.  This did shorten the lives of many.