What is the Worst Thing You Can Leave at Home While on Vacation?

Vacation season is winding down.  It seems like we always leave something at home that we were planning to take with us.  When we get back, we find it sitting on the bed, on the counter or in the garage.

Was there something you left home when you went on vacation?  Certain things, like a shirt or shoes, aren't too big of a deal because you can always buy them.  But how about a phone charger or a credit card?

What is the worst thing you can leave at home when going on vacation?