Trail map. Never count on trail signs to get you where you want to go. Signs get knocked down or disappear due to rain, wind, or visitors looking for souvenirs. Carry a more detailed map than the free one given out at park entrance stations. A variety of maps are for sale at park visitors centers and stores. Try maps published by Tom Harrison Maps or Trails Illustrated.
Extra clothing. Not only can the weather suddenly turn windy, cloudy, or rainy (it can even snow!), but your body’s condition also changes: You’ll perspire as you hike up a sunny hill and then get chilled at the top of a windy ridge or when you head into shade. Always carry a lightweight, waterproof, wind-resistant jacket. Stay away from clothing made from cotton; Once cotton gets wet, it stays wet. Polyester-blend fabrics dry faster. Some high-tech fabrics actually wick moisture away from your skin. In cooler temperatures, or when heading to a mountain summit even on a hot day, carry gloves and a hat as well.
Flashlight. Mini-flashlights are available everywhere, weigh almost nothing, and can save the day. Tiny “squeeze” LED flashlights, about the size and shape of a quarter, can clip onto any key ring. Make sure the batteries work before you set out on the trail. They are small so take along a few extras.
Sunglasses and sunscreen. The higher the elevation, the more dangerous the sun is. Put on high-SPF sunscreen 30 minutes before you go out, and then reapply every couple hours. Also protect your face with a wide-brimmed hat and your lips with high-SPF lip balm.
Insect repellent. Find one that works for you and carry it with you. Many types of insect repellent use an ingredient called DEET, which is effective but also quite toxic, especially for children should not use repellent with high levels of DEET, although it seems to be safe for adults. Other types of repellent are made of natural substances, such as lemon or eucalyptus oil. If you visit White Wolf’s meadows in the middle of a major mosquito hatch, it often seems like nothing works except covering your entire body in mosquito netting.
First-aid kit. Supplies for blister repair, an ace bandage, an antibiotic ointment, and an anti-inflammatory medicine such as ibuprofen can be valuable in emergencies. If you’re allergic to bee stings or anything else in the outdoors, carry medication.
Swiss Army-style pocket knife. Carry one with several blades, a can opener, scissors, and tweezers.
Compass. Know how to use it. If you prefer to use GPS , fine, but know that GPS isn’t going to work everywhere you go.
Emergency supplies. Ask, “What would I need if I had to spend the night outside?” Aside from food and water, these are supplies that will get you through an unplanned night in the wilderness.
- Lightweight blanket. Get a blanket or sleeping bag made of foil-like Mylar film designed to reflect radiating body heat. These make a great emergency shelter and weigh and cost almost nothing.
- Matches and a candle. Keep matches in a waterproof container (or zippered bag), just in case you ever need to build a fire in an emergency.
- Whistle. If you need help, you can blow a whistle for a lot longer than you can shout.
- Small signal mirror. A flash from a mirror can be seen from far away.
Fun stuff. These aren’t necessary, but can make your trip more fun: a wildflower or birding book, a pair of binoculars, a fishing license and lightweight fishing equipment, and extra socks (they feel like heaven halfway through a long hike).
Excerpted from the Fifth Edition of Moon Yosemite.