Enter the Disposable Flask ($15/set of 3). These 7.5 oz. reusable foil pouches are portable, freezable, pocketable, and easily disposable, and feature airtight plastic lids that won't leave tell-tale leakage marks on your clothes.
Jesus, why didn't I think of that? Oh right, I DID. They're called Zip-Loc bags, and I've been filling them with bourbon for years. Anybody need a nip? I have two. They're perky!
Disposable Flask [uncrate]
Thanks to naas, who just carries his bottles with him wherever he goes.