2. First Aid
4. Fire starter
9. Sun Protection
10. Emergency Shelter
Flashlight, headlamp, backpacking lantern-it does not matter as long as there is a way to light the darkness. LED bulbs of course, use much less battery life. If there is any chance the hike will involve a cave, have 2 sources of light. Even just a tiny flashlight on a key ring or as a zipper pull can save the day. Night. Trip.
2. First Aid:
At the very least:
Vitamin I (Ibuprofen or any OTC NSAID to reduce swelling)
bandaids (various types/sizes) and ointment
Leukotape OR Moleskin and small scissors (nail scissors work great)
A whistle is always good to have along, 3 toots at a time is a signal for help. Many pack makers are adding these to the sternum strap these days.
A couple protein bars, some trail mix (with nuts and dried fruit at least) or some other calorie-dense snack, think worst-case in this situation and imagine being stuck out overnight. If looking for a calorie count, 1200 is what a 150-pound person will burn walking 10 miles on easy terrain at a 2.5 MPH clip. If there will be lots of walking up hills, running, climbing or it’s below 40 degrees-take more calories.
Flint and steel, lighter, waterproof matches, it’s your choice. Some folks like to have along something to get the fire burning such as a film canister filled with dryer lint soaked in paraffin or a small fuel tablet are good choices. Always store it in a waterproof container or baggie.
If choosing to take a folding blade, be absolutely sure it locks tightly in place while open and is easy enough to close one-handed. A fixed blade is my personal choice.
Extra water or a way to purify water along the route. Full post about options here.
Protection from the elements! Rain gear, or at least a poncho, and a jacket. Most people eliminate the jacket in summer, but a lightweight down puffy will pack down to nearly nothing and can add comfort like nothing else if you end up lost or injured. Being able to keep warm and dry is essential.
At the VERY least-a trail map, even on your phone (or take a photo at the kiosk), is better than heading out simply planning to follow one trail or use blazes to navigate.
Next best, if available, would be the guidebook or databook for the trail.
GPS is wonderful, but battery life is ever an issue whether on a phone or independent unit.
Best case would be a topo map and compass (and the skill set needed to use them).
Sun hat, sunglasses, and sunscreen. A sunscreen tube, like a big chapstick, is great for the whole face, it can go on lips and tends to stay put under sweat.
A large trash bag and a space blanket, a bivy sack, a tube tent, or a lightweight tarp. Backpackers would have some type of sleep system along, so this is more for day hiking, but always have a system in place to keep dry.