This is especially good advice in regard to liquids. About a year ago we were connecting at LHR to BA from AA. My companion keeps a hotel room sized bottle of hand lotion in her jacket pocket, and has done so for years without being stopped, domestically or internationally. On this occasion she was stopped at the security checkpoint in T-5, and was detained for 25 +/- minutes, where her carry on and jacket were given something akin to the TSA’s SSSS treatment.

Fortunately we had ample time, so we were still able to visit the Galleries lounge before boarding our BA flight.