If you're short of brown sugar, you probably have granulated white sugar use that. White sugar should work as well as brown sugar in the recipe. Cookies may be crispier without brown sugar, but that's not a deal-breaker.
Muscovado sugar is unprocessed sugar cane with plenty of molasses, making it a good option for brown sugar if you want a strong taste.
Boiling and drying coconut palms provide coconut sugar. While it has similar calories as white sugar, it contains less fructose, making it a healthier alternative. This should be taken with a grain of salt as calories are calories.
By "blitzing" granulated white sugar with molasses, you may manufacture brown sugar at home. Brown sugar is just that. For light brown sugar, use 1 cup white sugar and 1 tablespoon molasses. For dark brown sugar, use 2 tablespoons molasses.
Maple sugar, made from maple syrup rather than sugar cane, gives a sweet, maple flavor to practically any dish. It's usually used to top oatmeal or porridge, but it may also replace brown sugar in baking.
Brown sugar may be substituted with white sugar and molasses, but honey, maple syrup, or agave nectar work too. To substitute a cup of brown sugar, add a tablespoon or two of liquid sweetener with a scant 1 cup of white sugar.
Instead of granulated sugar, you may use honey, maple syrup, or agave, but you'll need to adjust the recipe. Use 2/3 cup liquid sweetener for every cup of brown sugar and decrease other liquids by 2 tablespoons, such as milk.