I did my "half commute" today. I drive to a lot about 7.7 miles from work and ride in at around 6 AM. I am all clean and changed before most of my colleagues and the students arrive. On the way home, I take a longer route (slightly different each time) for variety. Today I clocked in at 19.6 miles, average around 15.
I have a smaller trunk bag and I wear a Camelback without the bladder in it to haul a few things (wallet, glasses, keys, make up, papers). It's not really heavy, but on the way home it does slow me down a little. I have my clean up supplies at school, along with clothes, so I don't have to haul them. My bike is too small for panniers.
Tomorrow will be my last ride on my bike. I am getting a new custom bike, with a Kuota (spelling?) frame on Thursday. Of course it is supposed to rain on Thursday and Friday, so I may be waiting to ride it.