All types of bags and totes are useful for carrying many different types of supplies and equipment. However, backpacks allow for items to be carried directly on the body while still allowing the free use of both hands. They are not just the preferred bag of mountaineers, but also of students, parents, daily commuters, travelers and many others. Different kinds of backpacks fulfill different needs.
Some travelers use backpacks to travel for up to a week or sometimes longer. Backpacking through Europe was once extremely popular and rucksack is the European name for a backpack. The types suitable for travel often feature hidden inner pockets to secure important documents as well as money or traveler's checks. Outer zippered pockets add convenient extra storage. Mesh pouches available on some backpacks allow temporary storage for wet items and many people use these bags as luggage for camping vacations or short hiking trips.
Daily commuters and students often prefer the kinds of backpacks that conveniently accommodate MP3 players and headphones as well as cell phones. Room for extra shoes and a lunch or snacks is also often desired by workers and students. Notebook backpacks are types that can store notebooks, textbooks and paperwork easily, and there are also others available to carry notebook or laptop computers and their accessories.
Children's backpacks are sized for toddlers to teens to carry and are often available in many popular licensed designs and trendy colors. Parents of young children and infants often use those that can hold diapers and accessories as they leave their hands free to push a stroller or hold a child's hand. Athletes such as snowboarders, skiers and cyclists may use backpacks to hold snacks and athletic gear. Some have outer pockets made especially to hold water bottles.
Messenger bags are not really backpacks, although they are convenient bags for those on the go. These bags are styled like a bicycle courier's bag and have a shoulder strap and a large rectangular bag space. They are usually worn across the body rather than on the back and are often waterproof.
The kinds of backpacks used for backpacking sports by mountaineers are often more rugged than other backpacks. These may have frames on them for extra support. Sleeping bags and other equipment can usually be attached to the frames on most types made for mountain climbing.