Longest day was 26 miles, on pretty flat ground. I carried a cast iron frying pan in a Trapper Nelson with no waistbelt. I haven't done any really long backpack trips.
Longest canoe trip was 151 miles. Longest horse pack trip was over 100 miles in a week, moving every other day. Longest canoe day was 36 miles. Longest horseback day was around 30-35 miles.
Sometimes it is not the mileage but the amount of hours involved. In rough country 10 miles can be a long day. Once at the end of a 10 day hunting trip in Colorado, we packed up and left at 0800. We got to the trucks after midnight. Lots of snow, darkness and plenty of mule wrecks along the way. A tough day, but one I will never forget. Was it 1985 or 1885?