The Commuter has pockets on both sides and on the flap, but none are big enough to hold a big u-lock; you'd have to store that in the main compartment. Arkel has many other bags that might serve your needs better. Other options include using a folding basket on the opposite side of the pannier for those grocery/beer runs. This is how I transport my u-lock:



I drop the "u" through the rack on the opposite side of the pannier and it's weight keeps it in place. It does rattle around a bit but a bungee cord would steady it if need be. A folding basket would conceivably still work in this configuration. I have one, but it's on another bike.