Mine varies depending upon where I'm heading but I do have a few standard items: wallet, keys, chap stick, eye drops, iPhone, tactical flashlight (Streamlight ProTac 1L) and a pocket knife (Kershaw Leek). I carry the specific flashlight because it's small but still has a strobe function (good for defensive situations) and I carry the specific knife because it's spring assist open for easy, one handed access and it has a partially serrated blade which makes cutting through difficult material (rope, seatbelt fabric, etc) much easier.
When I'm at work I don't take the knife though I probably could. I do have a small multitool that has a knife on it at work, though, and I load that sucker into my pocket when I may need it. I also have a Swiss Army knife that has a USB drive in it that I haven't gotten around to bringing in yet. At work, though, my kit can vary quite a bit and I wear cargo pants to accommodate it. Depending on what I'm doing I may need just a pen and paper, maybe my laptop, possibly some tools, etc - it all depends.
When I'm not at work I sometimes add a Glock 29 or 27 to the list. I prefer the 29 but sometimes I need the smaller piece. I also carry an extra mag with the 29 and occasionally with the 27.