This story at the Seattle Post-Intelligencer describes the so-called 10 Essentials for Wilderness Survival. On day hikes in good weather in the Bay Area you won’t need most of them, but it’s important to understand them. You can also buy survival kits that cover all 10 and toss them in your day pack.

There is some overlap with my Essentials for Happy Hiking, which are more geared toward day hikes where nothing goes wrong.
The P-I’s list:

  1. NAVIGATION.
  2. SUN PROTECTION.
  3. INSULATION.
  4. ILLUMINATION.
  5. FIRST-AID SUPPLIES.
  6. FIRE.
  7. REPAIR KIT AND TOOLS.
  8. NUTRITION.
  9. HYDRATION.
  10. EMERGENCY SHELTER.

I have a sealed tin from Tacoma Mountain Rescue that I hope to never use. You should at the very least carry something to treat blisters — moleskin and so forth. It can bring more joy to your non-hiking life.