The ability to make light.
The ability to make fire.
The ability to effect minor repairs.
A good blade.
The ability to call Scotty for beamout.
I'll add, the ability to write, find your way, know the time, and pull a splinter!
I always carry a Pockits Holster on my belt. It contains a Mini Mag with LED conversion kit, Gerber MultiTool, SwissTec 4 way screwdriver (Keyring clip removed), 3 Bandaids, a Bic Click pen, a Sharpie marker, and a pair of splinter tweezers. On the removable keyring is a tiny LED (like a photon) keyring light.
Cliped to my pocket is a Spyderco Rescue knife. Inside my pocket is a Zippo lighter. In my other pocket is a pocket watch and a hankerchief.
My key ring contains another tiny LED keyring light, as well as a SwissTec mini pliers tool, a tiny keyshaped knife, and a signal whistle with compass, and a pair of disposable foam earplugs stored inside the whisle's compartment.
My cell phone lives in a leather sleeve/holster that has a small carry strap attached. I cliped another tiny LED keyring light to the strap (You can never have enough keyring LED lights!)
In my wallet is a $25 phone card (in case my cell dies) as well as a small laminated emergency phone number list (again, in case my cell dies), and an Organ Doner card (in case I dies!) hehehe
I use my knife, Mini Mag, and Gerber almost every day!