Whether you're on a short hike or are trying to get out of the wilderness during a survival situation, you'll need a means of navigating. This means having a detailed topographic map of your location, and a compass. A USGS 1: 24,000 topo map of the area that you're trekking in is a good choice. A GPS is also a valuable tool, but because batteries have a limited life and such a tool may break, it should not be relied upon without a compass and paper map as backup. A barometric altimeter is another helpful navigational tool.
Protection from the sun is important year-round. Use sun block, lip protection, sunglasses and a hat to fully guard against the sun's harmful rays. Clothing that thoroughly shields your skin is also recommended.
Water is a top priority in survival situations. Always carry water on a hike. Having a sufficient supply, as well as a means of purifying natural water, is key. Filters are good for taking out large sediments and impurities, while purifying agents will remove microscopic organisms. Another option for purifying is to boil the water, in which case you'll need a metal container.
Maintaining strength and energy requires food. Bring food with you, and pack extra in case of emergency. Procurement tools including fishing line, hooks and a good knife. These are important provisions in any case, as they can be put to multiple uses.
Fire and Warmth
Fire is an important element of survival. You'll need it to keep warm, ward off predators, cook and boil water. To be sure you can always get a fire lit, pack waterproof matches, a lighter or other means of sparking a fire, and a dry fire starter. Additional clothing is important, in the event temperatures drop. Tailor your clothing to the season and the conditions of your trip. Don't forget rain gear. If you don't have a tent, an emergency shelter such as a bivy or reflective blanket can provide a some coverage from the elements.
A flashlight or headlamp is an invaluable tool for any activities after dark. Even if you make camp well before sundown, chances are you'll need some light at night. Carry extra batteries to ensure your light source lasts.
Hopefully, you'll never become injured in the outdoors, but if you do, you'll need a good first aid kit. Kits should include different types and sizes of bandages; gauze; disinfectant; tape; pain medication; tweezers; and scissors. Larger first aid kits include additional supplies. You must determine what's necessary for your specific trip. If you aren't familiar with basic first aid techniques, bring a first aid guide book. Many stores carry pre-assembled first aid kits, or you could build your own. Bring ample first aid supplies for the size of your group.
Multi-Purpose Tools and Repair
While the aforementioned items address tangible issues that you might face, multi-purpose tools are geared toward situations that you may not expect. They can help to perform many tasks in the wilderness and allow you to repair your equipment. Some important tools are a multi-tool, such as a Leatherman or Swiss Army Knife; duct tape; zip ties; cable; and repair kits for your particular equipment.
In the worst of situations, getting help from others will be a priority. Simple signaling equipment, such as a mirror and emergency whistle, can be easily carried. For more risky, extensive trips, a satellite-based communication device, such as a PLB or satellite phone, is another possible option.