Primary when at work is a SIG P229R in .40 S&W (because they issued me one and said I shall carry it in lieu of the lovely 1911 I was carrying at the time). BUG is any one of the off-duty guns listed below:
Walther PPK
Kahr PM40
Kel-Tec P3AT
S&W 31-1 2" (the only revolver currently in the mix)
Off-duty I carry some mix of two of the above, usually something and the Kel-Tec.
Normally, I carry one reload for each weapon, primary and BUG. The BUG is there because, among all the other reasons, if I wind up having to shoot, responding units (my own or those wherever I am) will have to take the gun I used. I don't want to find myself suddenly alone and unarmed and on my way home in sight of whatever friends the eejit who attacked me might have had nearby. I also keep a knife and some sort of yawara (Kubotan or suitable pen) at hand as well.