The Bit Buddy, from Huot Manufacturing, St. Paul, is a clip-on drill index holding 29 drills. Shaped like a cup with a screw-on domed cover, the drill-bit holder holds fractional drills from 1/16 ...

There are also generic pivoting bit holders available on Amazon, though you might not get as much quality out of these. One of the more popular versions of this concept is DeWalt's MAXFIT Pivot ...