Last month the agency that controls security aboard flights in Canada changed what passengers are allowed to bring aboard -- but the rules are different depending on destination.

The Canadian Air Transport Security Authority now permits small knives, with a blade of less than six cm, as a carry-on item for flights to Europe, but they will be confiscated from those heading to the United States.

Try to board and plane with a longer knife and it will be seized--in fact CATSA agents have seized at least two hunting knives, two utility knives, a folding saw blade and kitchen knives from passengers at Trudeau airport this week.

Other items seized this week include a hammer, a plastic toy gun, and a bottle-opener shaped like a bullet, which would have been accepted if packed and stowed as checked luggage.

One of the most common mistakes by passengers is bringing too many liquids. Every day CATSA confiscates bucket loads of items from passengers: mostly liquids, aerosols, and gels, which covers everything from a can of Coke, to a bottle of water, to lighter fluid.

While liquids are permitted there is a limit: 100 ml of any one item in a carry-on bag except for medication, baby food, formula and juice for children.

CATSA also now allows inorganic powders such as bath salts as a carry-on, as long as there is less than 350 ml.

The security agency expects that 25,000 to 30,000 people will travel through Trudeau airport on Dec. 21 and 22.

Mathieu Larocque of CATSA said most passengers know what to bring but find the reminders useful.

"When we survey passengers there's an increased awareness about these rules, however the number of passengers keeps going up," said Larocque. “Hundreds of thousands of travellers are going to go through our checkpoints and we want to make sure that they are aware of the rules.”

The holiday season adds another wrinkle for passengers, said Anne-Sophie Hamel of Aeroports de Montreal.

“For the carry on, all the gifts that you're bringing to your family or your close ones can't be wrapped because if you need to have extra checking in their luggage, they're going to have to rip them open. So that's not something that we want. So unless you're actually bringing socks to the security agent, don't wrap it!” she said.

The agency has also implemented a new security screening system this year that should help speed up processing.

Four passengers at a time can begin placing their belongings in a bin at the same time and thanks to the automated system, a new bin appears for the next passenger.

“So that saves us from having screening officers walk back and forth with bins,” said Larocque.