We’ve asked many a folk where they carry their flask and the answer is different if we ask a man vs a woman.
For men, the top three areas they carry the flask are in their breast coat pocket of a jacket, in their front pant pocket of trousers – typically, jeans are too tight for this, or in the top of their boot.
For woman, a purse or pack of some type is most common followed by jacket pocket. An honorable mention goes to those who have made or purchased contraptions to carry their flask discretely on person (i.e. garter belt, waist strap, etc.)