In the last year, 3 of my friends got their bikes stolen by leaving them "just for a minute" in front of a shop "while watching them through the window".
Nevertheless, sometimes I do the same. Maybe I didn't plan to bring a lock, and need to jump really quick to somewhere. Maybe there is a security guard nearby, or a bank camera. Maybe I am just too lazy to to dig the lock out of the bottom of my backpack, and have exact change to grab a beer. Maybe there is nowhere to lock to in a 100m radius.
My question is how to increase security in these dangerous situations.
A friend shared with me, that he shifts into the lowest gear - that way if someone tries to ride away the bike, it will take him quite some time. On the other hand, something that I do, is lean my backpack against the bike or even strap them together. IMO this makes riding off with the bike a little more difficult, while risking my backpack along with the bike.
Currently, the "derail the chain off the front chainrings" sounds most sane to me, because I can do it with my shoe, without getting oil on my hands. Still, carrying the lock on my waist, under the backpack belt, is the far best solution. Why do I even put it inside the backpack?