The parade of passengers as they board can be interesting to watch from the comfort of your seat, especially after you have safely accommodated your carry-on items and are no longer worried about running out of space. Some flyers sit in awe at the jaw-dropping items fellow passengers choose to bring on board.

We hear the announcements prior to boarding: "Each passenger is allowed on carry-on item, plus one personal item..." What exactly does that mean? Just about every airline clearly spells out the weights and dimensions of permitted carry-on bags, but they can be slightly more ambiguous about that extra "personal item." Carriers typically define a personal item as a briefcase, or a purse or handbag, or a laptop with case. They also excuse any items needed for mobility and health such as crutches and approved medical devices. But what about those that like to bring sporting gear or camera equipment or a library of books and an array of electronic gadgets, each with its own carrying case? Most of the time, airlines will look the other way. But you can't always be sure.

Some airlines will restrict your carry-on allowance to just one item, period. We like to think that most airlines policies are similar, but this could depend on your destination, type of aircraft, or cabin class. Rule number one: check with your carrier. Airline web sites are a good place to start. Even so, the details vary. Some carriers will give you weights and dimensions; others will just give you broad recommendations. Once you arrive at the boarding gate, you may find some agents insistent on placing your bags in a carry-on template to make sure they comply. You may also find some agents who simply are too busy to check.

Here are some examples of what you may find on an airline's web site:

United Airlines
For worldwide travel on any United flight, you may carry on one bag and one personal item such as a large shoulder bag, large backpack, briefcase, laptop bag or an item of similar size. Your carry-on bag...

• must fit under your seat or in the overhead bin;
• must not be more than 9 x 14 x 22 inches (23 x 35 x 56 cm) or 45 linear inches* (114 linear cm); and
• may be required to travel as checked baggage if the bag cannot be safely stowed on your flight.

The following items are not counted toward your one bag and one personal item limit:

• Overcoat or wrap
• Umbrella
• A reasonable amount of reading material
• Pet carrier (fees apply)
• A collapsible wheelchair
• Child restraint seat meeting FAA approval standards
• Camera
• Diaper bag
• A limited amount of duty-free merchandise or food purchased at the airport
• Assistive devices (a cane, one set of crutches, prescription medications and any medical devices needed to administer the medications, a portable oxygen concentrator (POC), etc.)

Qantas:
From 25 December 2009 the following items may now be taken through security screening points and into the sterile area of airports within Australia:

• umbrellas with metal points
• knitting and crochet needles
• pointed metal nail files (including nail clippers)
• corkscrews, and
• racquets used in squash, tennis, badminton or any other sport.

Note that these items may not be permitted on flights departing to destinations outside of Australia.

Emirates:
Generally, the amount of cabin baggage you may bring depends on which service class you are flying.

First Class and Business Class customers are permitted two pieces of carry-on baggage: one briefcase plus either one handbag or one garment bag. The briefcase may not exceed 18 x 14 x 8 inches (45 x 35 x 20 cm); the handbag may not exceed 22 x 15 x 8 inches (55 x 38 x 20 cm); the garment bag can be no more than 8 inches (20 cm) thick when folded. The total combined weight of both pieces may not be more than 26 lb (12 kg).

Economy Class customers are permitted one piece of carry-on baggage that may not exceed 22 x 15 x 8 inches (55 x 38 x 20 cm) and must weigh no more than 15 lb (7 kg).

Note: For customers boarding in India, the size of carry-on baggage may not exceed 45.3 total inches or 115 cm (length + width + height).

British Airways:
You are allowed one piece of hand baggage plus a laptop or handbag. A 23kg (51lbs) maximum bag weight applies and you must be able to lift the bag unaided into the overhead lockers in the aircraft cabin.

• Your main piece of hand baggage is up to the dimensions 56cm x 45cm x 25cm (22in x 18in x 10in), including the handle, pockets and wheels.
• Your bag must fit into the bag gauge, available at the check-in area.
• Your laptop or handbag is up to the dimensions 45cm x 36cm x 20cm (18in x 14in x 8in), including the handle and pockets.
• Your laptop or handbag must fit under the seat in front of you.

One trick that passengers like to use is the piggy-back pile on the one portable roller bag. As long as all their extra contraptions can be strapped to a single carry-on bag with wheels, airlines must consider this a single carry-on item, right? You might be clever enough to stuff your overcoat with all kinds of items to make it seem that you only have the one carry-on, but that bulky coat will need some storage room too. Check with your airline to determine what you're allowed to take on board with you. If you're allowed that extra personal item, make sure it's small enough to stow underneath the seat in front of you. Though flyers would prefer to use the space to take advantage of what little legroom there is in the small confines of an economy cabin, it's best to keep your electronic gadgets and other materials you will want to reach for during the flight close at hand. It's a new year, but old habits die hard.