Anyone traveling by air has to go through a security checkpoint set up to prevent terrorists from carrying prohibited items into the airport's secure sections or onto the airplanes. Airport security screens passengers and inspects their carry-on and checked luggage for contraband. Packing correctly helps the check-in process go more smoothly and rapidly.
For international flights, you must bring the proper papers---passports, visas and any other identification showing your citizenship and possibly the reason for your travels (travel visa, work visa, education visa). You may need to have paperwork declaring items being brought into the country that you didn't have when leaving that country, for duty payments. Have receipts for these items collected together.
You may carry medications as long as they are in their original bottles. Coats that cannot be packed and carry-on luggage must be X-rayed and stored in the overhead bin during flight. Purses and diaper bags are allowed as are a few toys or books to keep children entertained. Electronic items such as game or music devices and computers are allowed as long they can are turned on during check-in to prove that they are actually what they appear to be.
Liquids and sharp objects (knitting needles, sewing scissors and pocket knives) may be confined to checked baggage. Passengers should be familiar with items forbidden by the country they're traveling to. To speed X-raying, collect all bottles (3 oz. or less) in one clear plastic bag. It's better to pack liquids in checked luggage, however any that must be carried on (i.e. medications and baby formula) should be declared and should be limited to what you need during flight. Empty pockets of metal objects and PDAs, collecting them in a plastic bag to speed check-in.
Passengers should ascertain which items their specific airliners ban, such as compressed air cylinders, camping and paintball equipment or scuba gear. Other items will need advance authorization, such as pets and service animals, coffins and crematory containers. Matches and lighters will not be allowed in the cabin and must be packed in checked baggage. Prohibited items include firearms, domestic plants and animals and dangerous toys or other products which could cause injury. Also prohibited are illegal substances and hazardous materials (drugs and aerosol cans), as well as loose lithium batteries (due to explosion and flammability concerns).
Some clothing and accessories with a lot of metal may set off the metal detector. Avoid wearing heavy jewelry, clothing with metal like studs or chains and large belt buckles. Anyone with body piercings can request a private screening to remove the jewelry. The best advice is when in doubt, leave it out. If you will need it on the other end, you can buy it on the other end.
