From REI

The Ten Essentials
(for safety, survival and basic comfort)

1. Navigation
  • Map (w/protective case)
  • Compass
  • GPS (optional)
2. Sun protection
  • Sunscreen and lip balm
  • Sunglasses
  • Skin-shielding hat and clothing
3. Insulation
  • Jacket or vest
    (preferably synthetic)
  • Fleece pants (sometimes optional)

If you are out in winter you might want Blizzard Survival's Reflexcell emergency blanket with a honeycomb-like build is better than a single layer of reflective fabric.
4. Illumination
  • Headlamp or flashlight
    • Extra batteries
    5. First-aid supplies
  • First-aid kit (see first-aid checklist)
    • 6. Fire
    • Matches
    • Fire starter
      • Waterproof container
      7. Repair kit and tools
    • Knife or multi-tool
    • Mattress repair kit
      • Duct tape strips on bottle or poles
      8. Nutrition
    • Extra day's supply of food
      • Spare energy bars, gels, trail mix
      9. Hydration
    • Water bottle and/or hydration reservoir
      • Water filter or other treatment system
      10. Emergency shelter
    • (If no tent) tarp, bivy sack, reflective blanket

      • Other:

        Hiking Clothing
        Quick-drying pants/shorts Fleece jacket or wool sweater
        Short-sleeved shirts Wicking long underwear (top/bottoms)
        Long-sleeved shirts Regular underwear
        Warm pants (fleece or wool) Quick-drying swimsuit
        Fleece or wool vest

        Outerwear
        Rainwear (top/bottoms) Fleece or wool gloves/mittens
        Wide-brimmed rain/sun hat Waterproof gloves/overmitts
        Warm hat (fleece or wool) Bandanna

        Footwear
        Hiking socks Extra laces
        Wicking liner socks Gaiters
        Hiking boots/shoes that match the terrain

        Camping Gear
        Backpack Funnel
        Day/summit pack Matches/lighter
        Pack cover Cook set, dishes
        Tent, tarp or bivy sack Cooking/eating utensils
        Rainfly Drinking cup
        Tent stakes Pot grabber
        Footprints Biodegradable soap
        Tent broom Pot scrubber/dish towel
        Sleeping bag (in waterproof stuff sack) Plastic garbage bags
        Compression sack Resealable plastic bags
        Sleeping pad Water filter/purifier
        Sit pad or sleeping pad chair kit Water-purification tablets
        Extra nylon stuff sacks Water bottle(s)
        Food (adequate supply for your trip) Collapsible water container
        Stove and fuel Lantern

        Personal Items
        Toilet paper Lip balm (with sun protection)
        Toothbrush and toothpaste Insect repellent
        Small bath towel Head net
        Brush/comb Trowel
        Other personal toiletry items

        Other/Extras
        Altimeter Repair/sewing kit
        Binoculars 100-foot accessory cord
        Field guides Axe/saw
        Camera and film Money
        Notebook and pencil Photo ID
        Travel games Camping/fire permits, if needed
        Watch/alarm clock Fishing license
        Weather radio Trip Plan (left with a responsible friend)
        Hiking poles
        Links:
        REI: Ten Essentials, Adventure Travel Checklist, Backpacking, Backpacking: Repair Kit, Backpacking First Aid
        Ten Essentials at backpacking.net