You won't be able to carry a week's worth of luggage onto your plane (unless you travel really light), but all airlines allow you to bring a limited amount of baggage with you during a flight. Before you board you'll need to learn how big your bags can be and which items are allowed inside them.

Size Allowed

Policies for carry-on baggage can vary slightly among airlines based on the overhead space in the planes they use. Generally, your bag shouldn't exceed 22 inches long, 14 inches wide and 9 inches tall. Airlines usually provide a place to check the size of your carry-on near the check-in counter. If your bag fits in the hole, it is OK to take it onto the plane.

Number of Items

Most airlines allow you to bring onto the plane one carry-on item and one personal item. Personal items can consist of a wide range of objects and include purses, cameras, laptops and diaper bags. Such items as coats, magazines and pillows would not count toward either quota. If you bring a wheelchair or stroller to the gate, these items will be checked in there to allow easier access onto and off of the plane.

Forbidden Items

The Transportation Security Administration offers a list of generally prohibited items on its website. Generally, any item considered a sharp object, such as pocket knives, box cutters, scissors and razor blades (other than disposable razors) cannot be carried on, but can be checked with other luggage. The same goes for most firearms and ammunition, tools and martial arts weapons. You can neither carry on nor check most flammable and explosive materials.

Rules for Liquids

The TSA allows you to bring liquids, gels and aerosols onto planes -- but only in limited quantities. Place any of these materials you wish to carry on into one single quart-sized clear plastic bag to speed up the screening process. Each container, such as a can of shaving cream or a tube of toothpaste should contain no more than 3.4 ounces. You can bring more than 3.4 ounces of baby formula, medication and breast milk onto a plane, but you must declare them at the security checkpoint.