I ride almost the same distance, approx. 3.6 miles each way, and I spend maybe 10 minutes getting ready to ride at the end of my shift. As a chef, I don't really have the option of wearing my work clothes on my commute, but I don't get too technical about what I do wear. For most colder weather, I'm in jeans.
My ride is about 12 minutes in, 16 home. I'll wear the ipod some afternoons when I go in, but I don't want the distraction when riding at night. Water is completely unnecessary. Does anyone HAVE TO take a drink once every ten minutes or so?
I don't ride all out on my way in, so I keep from getting sweaty, and I know I'm going to take a shower when I get home, so I don't care. If anything, I might be a little uncomfortable for the first couple minutes or the last few minutes of my ride.
The bottom line for me is that I'd rather spend 5 minutes not being perfectly warm/ dry/ hydrated/ entertained than spend 25 minutes suiting up at the end of the night before I go home.