"Some people travel with weird stuff because they are collectors: it's an heirloom, they have ADHD [attention deficit hyperactive disorder] and it's their fidget, or they want to use the item as a training aid in a seminar," said Jeff Price, an aviation security expert and professor at Metropolitan State University of Denver.
Still, "a lot of people who don't travel frequently just don't understand that some of these items can be used as weapons," he said.
Passengers even have a hard time keeping known banned items at home, with firearms being wildly popular among seized items. As of Christmas Eve, the year's tally of firearms found at airport checkpoints was close to 3,900.
Next week, TSA officials are expected to release their official tally of firearms found in 2017, but the current number already significantly exceeds the total of 3,391 detected at airport checkpoints during 2016. The TSA reported that most gun owners claim they just "forgot" a firearm was in the bag they took to the airport.
According to TSA spokesman Mike England, one theory behind the increase in the number of firearms and banned items could be a function of more passengers at U.S. airports.
During the 2017 holiday travel period alone (Dec. 15, 2017, through Jan. 2, 2018), the TSA said it screened more than 42 million passengers and more than 30.6 million checked bags — a record. "More passengers equals more prohibited items," said England.
— Harriet Baskas is the author of seven books, including "Hidden Treasures: What Museums Can't or Won't Show You," and the Stuck at the Airport blog. Follow her on Twitter at
. Follow Road Warrior at @CNBCtravel.