I have a spare set of clothes at the office...

I don't really mind being wet much - it can be challenging when it's cold, but proper preparation can address that too. I use neoprene socks and shoe covers in cold rain, gore tex jacket, base layer polar tec stuff and a shirt (usually not even merino). The real challenge with rain comes with visibility and bicycle maintenance...you're a lot more susceptible to flats and you really have to clean your drive train, which is a hassle. I carry clothes in a pannier. I always use good lighting regardless, but I'm more careful in the rain, as well as being more likely to ride assertively in the center of a street.

I forgot to use a saddle cover today...