If you are walking, then a daysack of 25-35 litres should be sufficient.
We had porters to carry all our luggage apart from things like water that we carried in our day sacks.
This item is generally classified as a rucksack rather than a daysack because of its size.
There are times, especially in winter, when the average daysack just can't handle all you want to shove into it.
