In reply to Denni: If you break down in a blizzard, make sure you have your house keys in your pocket before the long walk home. Also, always keep a big mallet in the shed! (or alternatively a spare set of house keys, but where's the fun in that?)
Don't leave your car keys at work and your house keys in the car (me yesterday).
Maybe the best tip of all would be to get some new keys cut as spares, I'm sick of being locked out of the car or the house!
Oh, another good one for people with too much time on their hands. Fix a folded out coat hanger to some part of your cars exterior. Mines tucked under the back bumper and I'm anticipating the smugness I'll enjoy next time I drop my keys down a drain.