Airlines are tightening restrictions on carry-on baggage. Many now limit economy class passengers to one carry-on bag in addition to a briefcase or purse. These restrictions make it even more important to plan ahead, and make sure you can keep medicines, jewelry and other items of value with you, and not in a bag that might have to be checked. If the flight is not full, the airline may be more lenient, but don't count on it. First-class and business class travelers are often exempted from the more stringent restrictions.
Some airlines also make provisions for passengers belonging to their very frequent flyer programs.
These limits are set forth in each airline's Conditions of Carriage. Theft of portable computers, cameras and other small, valuable carry-on items from travelers is now common, particularly in busy airports. Do not leave them unwatched even for a short while. To avoid this scam, wait until you are next in line for the detector before putting your bag through the x-ray machine, and keep an eye on your bag as it comes out the other side. If you are traveling with someone, one of you can stay back with all the valuables to place on the x-ray reader, while the other can go through ahead and retrieve the items on the other side.