OK, this has been an interesting thread to follow, so I'll chime in. As far as tools, I tend to carry fairly light on my person and usually just have my Leatherman Blast. Sometimes I'll stick a spare 5 in 1 screwdriver in my pocket if I think there's a chance I might need it. I also always have at least one pen and at least one permanent sharpie (I'm kind of type A so I find myself needing to take a quick note or make a quick label almost as much as effect a quick repair to something). I also carry a lot of common small keys (CH751, EK333, etc) and find myself using them surprisingly frequently. Not quite to the level of Deviant Ollam's "open most things" keyring, but close.
My phone doubles as my flashlight when I need one quickly, so I don't carry a dedicated light anymore, though I used to.
Note, I am not a professional locksmith, though I work on them frequently and the above items tend to suit my needs for quick and dirty repairs/small changes on most mechanical things I come across.
