I was about to make the same suggestion. Not fast enough !
Your light is immediately available (usually the timer goes off when you are in the middle of the stairway, with big shopping bags in each hand...) <img src="/images/graemlins/crazy.gif" alt="" />
Another good point of that configuration is you have less risk to accidentaly power the LED light on inside the bag (being crushed between things)

While many people will not agree with the idea of constantly keeping a PSK on their person, such tiny LED lights are often well accepted.