The Alpkit Koala was just about big enough (read: almost too small) to fill it up properly with no movement whatsoever, best part is the bike doesn't feel any difference on the climb.
Staying at hostel mean just towel, toilette, cable lock, lightweight short and merino top, think it's 3ltr, idea for single or couple days night in hostel.
Rest of smaller item like snack, money, phone etc. In handlebar bag.
The Alpkit Koala was just about big enough (read: almost too small) to fill it up properly with no movement whatsoever, best part is the bike doesn't feel any difference on the climb.