I made these two simple keychain screwdrivers for your keychain. Both have a nice knurled grip for better traction.
The screwdriver.stl is a short bit holder that is designed for a bit to sit permanently in the socket. For me, it was a nice friction fit but if it falls out for you just use a bit of superglue.
The bit_holder.stl is a bit holder with a small magnet in the base to make fast and easy bit swaps possible. I used a cheap tiny neodymium magnet (4mm d; 2mm h) to hold the bit in place. The magnet is just friction fitted in there.
If you have any suggestion or questions; feel free to tell me.