Once bottled at the distillery, booze can have quite a long shelf life. However, once you start carrying it around in a flask, you’ll bruise it with all the shaking. If you’re carrying a flask of booze, you should be drinking the entire thing anyway – we’re only talking about 6 or so ounces of liquor. How long you carry it should not be an issue. But how long it will stay fresh is a matter of days, and at the most, a week. Once you fill your flask, you should be able to enjoy its contents in one or two outings without too much effort.