I have a kit that I keep in an old binocular case. It has a compass, fire tools, first aid, and survival gear(space blanket, needle and thread, wire saw, fish hooks, candle, etc.). With just that case I could make it 2-3 days if I had too. I wear a real small backpack(usually camelback) that I keep it in. Though very rare(once) I have unfortunately found myself afoot many miles from camp and I was glad I had it on my back rather than in my saddle bags.
The most used items have absolutely been the fire tools and blanket.
Whether I am going on a day ride or a multi-day trip I grab that case and I know I have the bare minimum covered.
Obviously I usually have many other items in my saddle bags/tied to the saddle etc... but the must haves are in that case or on my person (knife).
More important than anything else however is probably common sense and a basic knowledge of the area and country your riding in.
All the gear in the world isn't worth much if you don't understand how to use it and when.