I don't need the key on my house keychain and I'm afraid if I put it in a secret place in my purse I will lose or misplace it; but if I have to remember to bring it to work every day I'm bound to forget it... so I put it on a binder clip and clipped it to the inside of my work tote. That way I have it just when I'm going to work, and won't risk mixing it up with my other keys.
Of course I had to label the key, and any day I get to use my label maker is a good day.
This is super simple, just slide one end of the wire arm out, put the key on it, and put the wire end back into the clip.

