Why break your back carrying baggage when you've got a bike that's been designed to take the load? Whether you're packing shopping and school books, laptop and lunch box, or tent and touring gear, a rear rack is pretty much the best investment you can make – for both bike and back.
Most bikes these days can take some sort of rear pannier rack. If you're buying your bike from The Bike Shop, then look under the Bike Details tab for whether it can take a rack. If you're buying for a bike you've already got, you'll need to check for lugs on your frame. If you're not sure, please get in touch (email low res photos if you need).
Once you've converted to panniers, you'll wonder how you lasted this long!