Combine flavorings and alcohol in a clean quart jar. Screw on lid. Give the jar a good shake and set it in a cool, dark place for a few days and up to a week or two, shaking daily until you reach the flavor intensity you like.
Strain the spirits through a fine-mesh sieve, pressing on solids to release all of their juices, and then through a coffee filter to remove any sediment. Return spirits to the cleaned jar or other decorative food-grade bottle. Add sugar, if using, and shake to dissolve.
Spirits keep in a cool, dark place for up to a year; flavor improves with time.