i would suggest getting a few of those one oz bottles that they sell at the counter of all liquor stores. that's what they give you on planes anyway. then just grab a soda, mix up, and you're good to go. just make sure you put the liquor bottles inside of a zip lock bag so that you don't have any problems at security.
that's what i always do, but more so for the cost being that I'm more than legal age.