Hard Case/Secure Panniers
I'm curious to know whether any company makes hard case, locking bike panniers. I would love to run errands on my bike, but I often stop at more than one place when I'm out and I need a secure place to lock up the things I pick up along the way. It would seem obvious to make a secure, lockable pannier, but I can't find one anywhere.
One less car
If I'm running errands locally, I'll just take my pannier with me. It's very easy for me for my Carradice panniers as it kind of has a quick-release for the hooks on the rack.
If you're talking more long term storage, you might want to check out
they make some steel mesh security things that will prevent some thiefs, though it might also attract attention too. I've used it before when backpacking and having my backpack through security (many years ago).
Otivia and Ortlieb both make hard shell panniers.