What are you talking about? The OP said "Just buy one after screening, put it away in a bag and off you go." How is the OP going to buy your sinister "reactive liquids that are clear" after the screening checkpoint? How is the guy/gal who bought the Starbucks in the sterile area going to do anything sinister with it, except perhaps burn his throat if he drinks it too fast?

People need to get a grip -- and that includes FAs (no offense meant, skylady).