The only bike-specific thing I keep at work is a spare tube and patch kit, just in case I had a puncture on the way to work. (Upon checking, though, just a 700C tube. I should bring in a 26" and 650B tube just to have all my bikes covered.)

I've thought about getting extra phone/light chargers to leave at work, but haven't gotten around to it yet. I'm pretty obsessive about charging those things at home.