Backpacking is the outdoor recreation of carrying gear on one's back, while hiking for more than a day. It is often but not always an extended journey, and may or may not involve camping outdoors. In North America tenting is common, where simple shelters and mountain huts found widely in Europe are rare. In New Zealand, tramping is an equivalent term though overnight huts are frequently used.Hill walking is the equivalent in Britain, though backpackers make use of all kinds of accommodation, in addition to camping. Backpackers use simple huts in South Africa. Similar terms used in other countries are trekking and bushwalking.
Backpacking is an outdoor recreation where gear is carried in a backpack. This can include food, water, bedding, shelter, clothing, stove, and cooking kit. Weight is necessarily key. Backpacking trips consist of at least one night and can last for weeks or months, sometimes aided by planned resupply points or drops.
A skilled backpacker minimizes their impact on the environment, including staying on established trails, not disturbing vegetation, and carrying garbage out. The Leave No Trace movement ethos is direct: "Leave nothing but footprints. Take nothing but photos. Kill nothing but time. Keep nothing but memories".
Backpackers must always be prepared for difficulties, whether mishaps are experienced or not. These include adverse weather, difficult terrain, treacherous water crossings, heights, dangerous animals, dehydration, heat exhaustion, hypothermia, altitude sickness, illness, fatigue, injury, disabling waterborne diseases, and anxiety. The remoteness of backpacking locations can exacerbate any mishap. Survival gear and the skills to use it are paramount.
Backpacking camps are usually more spartan than campsites where gear is transported by car or boat. In areas with heavy backpacker traffic, a hike-in campsite might have a fire ring (where permissible), an outhouse, a wooden bulletin board with a map and information about the trail and area. Many hike-in camps are no more than level patches of ground free of underbrush. In remote wilderness areas hikers must choose their own site. Established camps are rare and the ethos is to "leave no trace" when gone.
In some regions, varying forms of accommodation exist, from simple log lean-to's to staffed facilities offering escalating degrees of service. Beds, meals, and even drinks may be had at Alpine huts scattered among well-traveled European mountains. Backpackers there can walk from hut-to-hut without leaving the mountains, while in places like the Lake District or Yorkshire Dales in England hill-walkers descend to stay in Youth hostels, farmhouses or guest houses.
In the more remote parts of Great Britain, especially Scotland, bothies exist to provide simple (free) accommodation for backpackers. On the French system of long distance trails, Grande Randonnées, backpackers can stay in gîtes d'etapes, which are simple hostels provided for walkers and cyclists. There are some simple shelters and occasional mountain hut also provided in North America, including on the Appalachian trail. Another example is the High Sierra Camps in the Yosemite National Park. Long distance backpacking trails with huts also exist in South Africa, including the 100 km plus Amatola Trail, in the Eastern Cape Province. Backpacking (trekking) is also popular in the Himalayas, where porters and pack animals are often used. 
Backpacking gear begins with a suitable backpack, proper both in size and fit. Next is clothing and footwear appropriate for expected conditions. Third is an adequate amount and type of food. Fourth is some form of sleep system (typically a sleeping bag and perhaps a foam pad). Fifth is some amount of survival gear, once again appropriate to the planned trip and skill-level of the backpacker. After that, everything is optional.
A shelter appropriate to expected conditions is typically next. Practical items not already mentioned - cook kit, stove, container for water, a means of purifying it - are characteristically but not always taken in some form. Depending on the trip ready-to-eat foods may suffice and suitable water be found along the way. More minimalist backpackers find ways to do with less.
Weight is always critical. A rule of thumb suggests a fully loaded backpack should weigh no more than 25% of a person's weight. Every single item is scrutinized, many removed the first time a pack is hefted. Lightweight gear is widely available, which may or may not sacrifice utility and durability but will almost always cost more. A wide variety utilizing carbon fiber, lightweight alloys, specialty plastics, and impregnated fabrics is available.
Proper hydration is critical to successful backpacking. Depending on conditions - which include weather, terrain, load, and the hiker's age and fitness - a backpacker needs anywhere from 1/2 to 2 gallons (2 to 8 liters), or more, per day. At 1 kilogram (2.2 lb) per 1 litre (1.1 US qt) water is exceptionally heavy. It is impossible to carry more than a few days' supply. Thus provisions for adequate water on a backpacking trip must be made in advance, whether that is knowing of potable sources such as lakes, streams, and springs en route or a means of filtering or purifying tainted water supplies as encountered.
Water may be stored in appropriate bottles or collapsible plastic bladders. Hydration packs are increasingly popular.
Backpacking is energy intensive. It is essential enough food is taken to maintain both energy and health. As with gear, weight is critical. Consequently, items with high food energy, long shelf life, and low mass and volume deliver the most utility. Satisfaction is another consideration, of greater or lesser importance to all hikers. Only they can decide whether it's worth the effort (and trade-off against other gear) to carry fresh, heavy, or luxury food items. The shorter the trip and easier the conditions the more feasible such treats become.
In all cases, both kit and fuel necessary to prepare and serve foodstuffs selected is part of the equation. Small liquid and gas fueled campstoves and ultralight cooking pots are the norm. Increasingly campfires are prohibited.
While most backpackers consume at least some specially prepared foods, many mainly rely on ordinary low moisture household items, such as cold cereal, oatmeal, powdered milk, cheese, crackers, sausage, salami, dried fruit, peanut butter, pasta, rice, and commercially packaged dinner entrees. Popular snacks include trail mix, easily prepared at home; nuts, energy bars, chocolate, and other forms of candy for quick energy and satisfaction. Jerky and pemmican are high-energy and lightweight. Coffee, tea, and cocoa are common beverages.
Domestic items are typically repackaged in zippered plastic bags. Canned or jarred food, except for meats or small delicacies, is avoided: their containers and moist contents are usually heavy, and the metal or glass must be packed out. Food dehydrators are popular for drying fruit, jerky, and pre-cooked meals.
Many hikers use freeze-dried precooked entrees for hot meals, quickly reconstituted by adding boiling water. An alternative is Ultra High Temperature (UHT) processed food, which has its moisture retained and merely needs heating with a special, water-activated chemical reaction.
These have roots in the U.S. military's MRE, and eliminate the need for a stove, fuel, and water. Against this, they are heavy, the water is already in the food, and they require their own fuel. Still, they have some attractions. They:
MREs can be difficult to find in retail stores, though a good selection is often available in a (U.S.) military surplus store.
Specialized cookbooks are available on trailside food and the challenges inherent in making it. Some focus on planning meals and preparing ingredients for short trips. Others on the challenges of organizing and preparing meals revolving around the bulk rationing prevalent in extended trail hikes, particularly those with pre-planned food drops.
Winter backpacking requires a higher level of skill and generally more specialized gear than in other seasons. Skis or snowshoes may be required to traverse deep snow, or crampons and an ice axe where needed. Winter sleeping bags and tents are essential, as are waterproof, water-repellent, and moisture dissipating materials. Cotton clothing retains moisture and chills the body, both particularly dangerous in cold weather. Winter backpackers stick to wool or synthetic fabric like nylon or polypropylene, which hold less moisture and often have specialized wicking properties to dissipate sweat generated during aerobic activities. Layering is essential, as wet clothes quickly sap body heat and can lead to frostbite or hypothermia.
A winter bivouac can also be made in a snow cave. It has thermal properties similar to an igloo and is effective both at providing protection from wind and low temperatures. A properly made snow cave can be 0 °C (32 °F) or warmer inside, even when outside temperatures are -40 °C (-40 °F). It is constructed by excavating snow so that its entrance tunnel is below the main space in order to retain warm air. Construction is simplified by building on a steep slope and digging slightly upwards and horizontally into the snow. The roof is domed to prevent dripping on the occupants. Adequate snow depth, free of rocks and ice, is needed -- generally 4 to 5 ft (1.2 to 1.5 m) is sufficient. A quinzhee is similar, but constructed by tunneling into mounded snow rather than by digging into a natural snow formation.