Anne Taintor flasks at a great vintage store, and for whatever reason, did not purchase one right then. I've actually thought back to that a few times - one of my regrets in life, not getting that flask when I had the chance.
Anyway, a flask has finally made it to my holiday wish list. She's designed several great ones to choose from; I'd actually recommend looking over her whole site for some giggles. On looking through them today, I'd definitely choose 'everything matches after four martinis,' but feel free to send me a different one if you really think it would be better for me.
As I said, my flask will usually contain Southern Comfort. While I've gotten bourbon or whiskey plenty of times at a wedding or other occasion for an open bar, the SoCo is always my favorite. What would your flask contain? And what the best reason to carry it?