Back Packs are a necessity of bicycle commuting but it is much nicer to ride without one.
I always get carried away with what I carry. In my pack I would carry a computer, computing gear, food, cloths, sometimes shoes, books etc. Sometimes the pack weights between 20 and 30 pounds which is more than my bike. This not only slows you down but it is uncomfortable and might even hurt your shoulders.
The trick is to try to keep your pack as light as possible. Only haul necessities to and from work. Try to keep less than 10 pounds in the pack.
Make sure a lot of thought goes in to your pack, the ultra cheap pack packs don’t have proper padding or airflow…. Buy a good one… it will cost over $100.00.