I've been carrying a little bourbon with me for a while now. It's been consumed on board and replenished a number of times, no worries. You just need to be discrete about it.
I've also got a flask, it's two 3 oz mini flasks that fit together in a sleeve that I've been thinking about taking, just for the fun of it. They're stamped "3 oz." on the bottom. Anyone try this one?