I only ride for leisure so I would never leave the bike for longer than it takes for me to go inside and buy something or go inside and take a pee. If possible I would never lose sight of the bike but sometimes I would take a dirt cheap lock I got from the supermarket bike section. It will not stand up to any serious attempt to break it but I would never be out of sight long enough for a serious attempt to be made without having enough time to rush out and give the bike thief a dose of woopasss.

Don't steal bikes bro! Not cool.