1. Map
2. Compass (optionally supplemented with a GPS receiver)
3. Sunglasses and sunscreen
4. Extra food and water
5. Extra clothes
6. Headlamp/flashlight
7. First aid kit
8. Fire starter
9. Matches
10. Knife
Woops, I rarely carry more than 4-5 of these.
Learning the knowledge of the area before hand, I don't carry a compass or Map, (If on trails).
I usually go cold food and there aren't too many places in California that you can start a fire at any way, so no matches or fire starter.
I never carry a knife; never use it, maybe to clean my fingernails.
Extra clothes- Not really necessary if you have a warm enough sleeping bag along with good rain gear, right? (and you don't do anything stupid).
Extra food- Only if I am in the middle of nowhere.
First aid kit- Same as above, maybe some tape for the feet if I'm out for more than 3 days and I'm pushing some technical trails.
I only 2 things I consider essentials that aren't on the list are.
1. Insulation for head.
2. Water purification.
People are too needy.