You have two options: get a second set of arms surgically added onto your shoulders to help carry your groceries, books, and beer, or attach the Portland Design Works Loading Dock Rear Rack to your commuter. If you opt for the latter, you'll be stoked on the light and strong aluminum frame, double-ply bamboo deck, and 35lb weight capacity. The Loading Dock attaches to a combination of seat stays and rear dropout mounting bosses with four bolts and seat stay clamps, so it'll fit any bike with the requisite eyelets and clearance.
Double-ply bamboo tray
Adjustable deck angle
Two seat-stay clamps
Familiarity: I've used it several times
Love the look of this for an older road bike I have and it sets up easy. Easy for making my road bike into an every day machine