Lock. I've been riding my bike from the (cheap parking) garage to the station each day. It's only a bit more than a mile, so it's not really "commuting".
This morning, went out to get the bike and found my Kryptonite lock thoroughly frozen.
If I'd have taken the time to get a hair dryer or heat gun hooked up... I'd have been late.
Have to shoot it full of WD-40 when I get home.