I travel with a Thermos mug, originally for use in hotels who seem to think a thimble of tea is enough (it isn't). Empty and open through security then fill it up at a cafe or lounge. Never been an issue (obviously look out for airports with at gate security). Excellent seals and saves waiting an eternity for BoB or service on long-haul.
https://www.thermosonline.co.uk/stor...7L-Blue/sp_644