I commute with a bag, but I guess I don't carry enough in it to have ever had a problem. I usually bring my wallet, keys, phone & a change of clothes. If I go into a store, everything except the clothes goes into my pockets. If I know I'm going to the store after work, I'll leave my change of clothes at work & pick it up the next day. I have 2 smaller packs (a Mountain Hardwear Scrambler & a golite ion) that will fold up very small. I then stuff them in my pocket or into my water bottle holder.