I've been rear-ended (get your minds outa the gutter) in a car sitting at a red light, and a friend of mine was stopped behind a school bus on his bike - some idiot was coming up fast behind him, so he gunned toward the ditch & joker plowed into the back of the bus.

I always keep my bike in gear at lights.

Shifting always works best when moving.  If you're stopped and didn't shift to 1st already, don't stomp the shifter to make it shift.  Instead, try feathering the clutch to engage the current gear and then try shifting to the next one... lather/rinse/repeat until you reach 1st gear.  Stomping will just wind up bending a rod in your linkage and then you won't be able to downshift at all.  It's a relatively inexpensive part (about $5, if I remember correctly) and I keep a spare since I bent mine once, but it's cheaper and easier to avoid replacing it at all.