my husband commutes 25 miles (50 miles round trip) 3 days a week. On monday he takes 1 pair of pants in and keeps his dressier shoes and the pants in his cubicle to wear those commuting days. He packs on a rack his work shirts, dress socks, lunch and whatever else he thinks he might need.

If you cannot mount a regular rack on your road bike, try a good sized handlebar bag. Backpacks are VERY hot in the heat, but could be successfully used during good days in the winter.