I am looking to buy a rucksack. I want to move quickly and pack minimally on a week-10 day long trip so I"m tempted by packs around the 45-55L range. However, I want to get a pack that is also versatile and there will be times in the future where I will want to go for longer trips. Packs are expensive so I want to make sure that I buy one that covers what I want to do. What is the extra affordance of packs with greater capacity that round the 55L mark.
In the 55L pack I am planning to fit Sleeping bag , Mat, Cotton shirt, Hiking trousers, socks, Underwear, Sunglasses, Suncream, Swim trunk, micro Towel, Sandals, Buff hat, Multi fuel, Mess tin, Utensils, Food, Water, Water carrier , Camelback / hydration pack, Bivvy bag , Camera , Backup battery , iPhone, iPhone rugged case, backup , walking poles, Solar charger , Backup battery: , Maps, Notebook?, GPS, batteries, Pens / pencils, Multi tool.