Long slender screwdriver with standard handle.
I needed a set of small screwdrivers for my bicyle repair toolkit. I wanted maximium versitility in the smallest space. Stores sell combo bits and bit drivers, but most have huge handles and won't fit in my toolkit.
3D printer to the rescue! I designed a medium sized slender handle and printed it up. It works great. The design borrows heavily from this blender tutorial, with some changes and enhancements: http://pages.uoregon.edu/art3d/driver/driver25.html
1) Print handle (I used ABS)
2) Purchase bits
3) Drive screws
I recommend that you print the first 1/2" (1 cm) or so and verify that the bits fit correctly. You can use the scale feature of your host software or slicer to adjust the hole size, since no other dimension really matters.
You can either purchase the extra long bits like I did or get a magnetic bit holder extension and glue that into the handle. The bit holder will probably work better if you plan on changing the bits often.