I try to keep my keychain as small as possible. So I have a house key, a work key, and a USB key (super tiny). Since I can bike to work, I don't carry a car key unless I have to. That's it!
As for as everything else? Nexus 5 phone, Moto360, a little bottle of various meds, another med, diphenhydramine pen, eyedrops, a multitool, wallet, glasses, glasses wipe, probably some change, clothes. And yes, I have to carry all that med crap, which means I pretty much have to carry the dreaded "fanny pack". At least it is small and leather; without it, leaving would be far too involved and I wouldn't have enough pockets.
If going outside for a while, then hat (cap), and prescription sunglasses too.... that is fun, since they are curved and not compact (love them, though). Sometimes I carry my Nexus 10, also.
It is always too much stuff :(