30 liters is the golden mean for day hikes: enough space to store a thick rain jacket, a thermos with hot soup, a snack (e.g., bread, nuts, or energy bars), a first-aid kit, a map or a GPS device, a change of clothes (e.g., a warm fleece), and even small outdoor accessories (like gloves or a hat). Yet, it's not so large that it weighs you down or throws you off balance while climbing – ideal for both experienced hikers and beginners who want to bring their essentials without being overwhelmed.
The best thing about the backpack? Its many intelligent pockets that prevent chaos inside and give you quick access to the things you frequently need