Hi. Since I hike a lot in the mountains, I'd just like to tell you my experiences. I have three backpacks. First is 15 l, I use this for shorter hikes mainly in summer, just for 2-3 t-shirts, binoculars, water and camera, and some small stuff. Second is 35 l, I have this for one-day longer trips, for at least three changes of clothes, some snacks, a can of b... and obligatory "flask". Third has 60 l, I use this for two or three day trips, e.g. Triglav, into it goes more clothes, some food and other necessities needed for a couple days. When buying a larger backpack (35-60 l) pay attention, it should have a removable cover on the bottom side with which you can immediately protect it in case of rain !!!!! Otherwise you have to buy it separately !!! And also pay attention that the backpack has as many pockets and straps as possible for attaching poles, crampons, ice axe, phone, camera, helmet, for water, etc. Hope I helped you a bit, choice is of course yours, best regards m.