Bike security is not too much of a concern for me.
My riding does not have me leaving my bike out of my sight very often. If I do leave my bike only when I run into restaurant or grocery store while touring or training. I do not want to carry a heavy lock or cable but wanted something that would, as the say, "keep honest people honest" . My thought was just to have something that would keep the bike from 'rolling away'.
For the past two years I have been using Planet Bike's Seat Leash for my security. It is lightweight and easy to carry. I can lock the frame to a secure item or just loop the cable through the rear wheel and bike frame. So far I have had no issues.... but then again, I do not use this for real "security" .
The seat leash with lock coiled up and easily attached to the Acorn Bag is pictured below.