Lee Valley Pocket Screwdrivers
These pocket screwdrivers have the size (and shape) of a quarter. The edge is shaped like a ramp so they can be used for different screw sizes. The range of edge thickness goes from 0.030" to 0.090". They are specially good for flat screws but can be used for Phillips too. They work reasonably well when you don't have a real screwdriver handy.
The Lee Valley Pocket screwdriver replaces dimes, quarters and table knives, or finger nails. Toss a few in the cutlery drawer to discourage you know who from using cutlery for household repairs. You can carry them in a keychain, wallet, etc. You can buy them buy the dozen at at Lee Valley's web site.