I use a Carradice saddlebag and I love it. It would be hard to carry a laptop, but for a fairly basic change of clothes and assorted tools it's great. I can even add my 5 frozen lunches on top once a week. Extremely waterproof, easy to take off if you want to slim down for weekend rides, excellent weight distrubution on the seat post under the saddle. It's very balanced, has minimal air drag and is easy to climb with. Frankly I never even notice it's there.