Try a standard backpack from Walmart. Put your gear in it, then place it on the rack flat (will hang over back at first). Fold the top third down so that it no longer hangs over the back. Bungee cord that down. Result: square-ish pack, that looks like a more expensive rack accessory. Another advantage: removes easily from rack, and easy to carry to the workplace / school (on your back). Ride to work without a sweaty back. Discovered this this morning, when I took slacks, dress shirt, and tie rolled and packed away, and wore a tie today for first time after a commute (showered and changed first though). Schweet.