I also commute with quite a bit of stuff. I have to carry a laptop, it's attachments, a breakfast and lunch, and anything else I might need throughout the day. I prefer to use a back pack to do this. The way I handle the cargo is to remove my seat and slide the pole through the top handle of my back pack. Once I lock the seat back in place this guarantees my bag wont fall off the bike. Then I strap it to my rear rack with bungy cords. Sometimes my food gets squished, but it's worked well otherwise.