A colleague recently visited a Department of Energy site to complete some contract work. As a matter of procedure, his rental car was thoroughly searched when he entered a restricted part of the facility. The search turned up a one pound bag of marijuana stuffed in the map pocket of one of the car's back passenger doors.

Long story short, the local authorities concluded that the grass was either left in the car by the previous renter or simply stashed in the rental car by someone at the airport for safekeeping. It took two days and a $1,000 in legal fees before that conclusion was reached.

Be sure to spend a few extra minutes looking over your rental car before you depart the lot. It's worth the effort.