You could do what I did today - I set my bike outside Jack in the Box and could see it through the window the whole time I ate. Only one guy stopped and looked at it for awhile which made me slightly nervous but he moved on. Luckily I remembered to remove my Edge 500 and since I have no seatbag there was nothing else to take other than the bike itself. I figured even with biking shoes I could get out there within 10 seconds and chase the culprit down.