Thanksgiving weekend marks one of the busiest flying seasons of the year. If you're among the passengers waiting in a long airport security line, be prepared by knowing the rules (and practicing patience with those who don't). Here's a refresher. I offer it now because holidays bring out the travelers in us all — even those who seldom fly.

Most airlines allow one carry-on plus a personal item. That does not mean a carry-on suitcase and a supersized shopping bag full of presents. Purses, diaper bags, briefcases and other similarly small bags qualify as a personal item.

Also, beware the size of your carry-on luggage. Airlines such as Delta, United and American have been quietly changing their baggage policies, reducing the size of carry-ons allowed onboard. On Delta, for instance, if you want to wheel a bag on board, it "may not exceed 45 linear inches," and must "fit easily in the Carry-on Baggage Check (approximately 22" x 14" x 9")."

Airlines began cracking down on oversized carry-ons last summer, when some fliers were forced to check bags they had previously carried aboard with no problem. Perhaps it was the airlines' way of preparing us for the holiday crackdowns to come.

The Transportation Security Administration's liquid rule for carry-ons remains in place. It requires that all containers of liquids, gels, aerosols, creams and pastes hold 3.4 ounces (100ml) or less. Those containers must be in the same quart-sized, clear, plastic, zip-top bag. Each passenger can carry only one such bag. So you have a 7-ounce tube of toothpaste that is almost used up, clearly holding no more than a squeeze? It won't fly — literally. Staunch compliance to the so-called 3-1-1 rule by fliers can help those checkpoints run smoothly.

Send your questions or tips to travel editor Kerri Westenberg at travel@startribune.com, and follow her on twitter @kerriwestenberg.