Two years ago I took an international flight with no checked luggage and had a bottle of mouthwash in my bag. (I'm used to this brand of mouthwash and apparently it's not available outside my own country).
The security guy found it and said it was forbidden aboard the plane for security reasons, except if I had a prescription.
I didn't have a prescription. So he threw it away. I thought "next time I will".
Now before taking a flight I just print a "prescription" with a random doctor name, saying in so many words that his patient (me) needs this mouthwash to travel, and sign it myself with a big, illegible signature.
I have used this meaningless piece of paper all over Europe, the US, Africa and it never failed to work.
Let's just hope the bad guys don't have access to a printer.