The nice thing about the Business Pannier by Inertia Design on workbycycle.com, is that the bungee mounting system is attached to a panel that the pannier zips to. You can zip your brief case off the panel and leave the mounting hardware on your bike. If you're not able to leave your bike in a secure place, you can unhook the panel from your bike and slip it into a pocket on the back of the pannier so you don't have hooks rubbing against your leg or catching on your clothes as you carry it around. It's a well designed system that doesn't come with a high price tag.