I used a REI backpack for carry-on for quite a while, like for five years or so. Regular, frequent travel, usually originating from DC airports - BWI, IAD, DCA. Near the end of that time, I was stopped at security in Pensacola; because of the pocket knife buried in one of the interior pockets, where it had been for the previous five years.
In addition to the Washington DC airports, I'd been through Charlotte, Denver, Seattle, LA, Phoenix, etc., etc. . . My son speculated that TSA was probably a pretty decent job for the Pensacola area, where the economy wasn't so strong, and likely people who gave a sh*t about doing a good job were more abundant in the candidate pool.
The guy was cool about, treated it as an honest mistake, and I handed it off to my son to take home.