The Transportation Security Administration (TSA) maintains a complex system of rules for transporting both carry-on items and checked bags on flights. Some objects are prohibited on planes at all times, while others may be checked and not carried, or vice versa. Confused? "When in doubt, leave it out," says the TSA.

If only it were that simple. Packing the wrong thing in your checked bag has the potential to ruin your trip—especially if that bag gets lost, broken, or roughed up by baggage handlers. A simple rule of thumb: Pack anything of value or importance in your carry-on bag, in case your luggage gets lost by the airline. But there's more to keep in mind. Here, in no particular order, are 10 things that you should always leave out of your checked bag.