Sake is a traditional Japanese beverage made from fermented rice. It boasts a slightly sweet flavor and a higher alcohol content than most wines (ABV 15% to 20%). While delicious to sip with a meal, sake is often used in marinades, sauces, soups, and other recipes to add delicate flavor depth and tenderize meats.
However, if you find yourself wanting to make a recipe that calls for sake, but not wanting to run to the store to grab some (or have problems finding sake in your local grocery store or Asian market), a fortified white wine, like dry vermouth, will do the trick.
You can also use Chinese rice wine, or dry sherry if the recipe only calls for a small amount (1 to 2 tablespoons) of sake. Or if you want to leave booze out of the equation all together, you can substitute rice wine vinegar mixed with water or white grape juice for the sake at a 1 to 3 part ratio. For example if a recipe calls for 1/4 cup sake, I would substitute 1 tablespoon rice wine vinegar mixed with 3 tablespoons water or juice.