The Ten Essentials for hiking include:
Map & Compass
Extra clothing (rain gear, hat, gloves, warm light coat or sweater).
Headlamp or flashlight
First-aid Kit (more than just a few Bandaids)
Fire Starter Kit (matches + butane lighter + fire starters)
Pocket Knife (Swiss Army Knife or Leatherman Multi-tool)
Water in an unbreakable container
Small metal pot or big metal cup (for melting snow)
Siltarp or Space Blanket + 50' x 1/8" Woven Nylon Chord
1/2 Foam Pad
In addition I always carry a Bandanna, Toilet Paper and Sunglasses.