(Besides pouring it down the drain.)
Compost It. If you compost — and seriously, why wouldn’t you? — just pour the coffee on the compost pile, which needs moisture in order to turn your kitchen scraps to rich garden soil. I also sometimes, lazily, pour the coffee straight into garden beds, like our starter blueberries, which need more acidic soil. But don’t tell any real gardeners. (And if you compost, throw the coffee grounds, filter and all, in the compost.)
Make Coffee Ice Cubes. Oldest trick in the book, but just freeze leftover coffee in an ice-cube tray. These are great when an occasional recipe calls for coffee, and also great in iced coffee because they won’t dilute the drink. Which leads me to…
Make Iced Coffee. Just put the leftover coffee in a pitcher in the fridge and drink it later. Preferably sitting outside with a book, mingling with the ducks.
Marinate Meat. My favorite pot roast recipe is browning a 3-pound roast in a dutch oven, then putting a sliced onion under it and a sliced onion above it, and pouring on a marinade of 1 cup coffee, 1/4 cup soy sauce, 2 crumbled bay leaves, 1 minced garlic clove, and 1/2 teaspoon dried oregano. Bake this, covered, in a preheated 300-degree oven for 3 1/2 to 4 hours. The coffee helps open up and tenderize the meat while it cooks, and that simple marinade makes it super-delicious.
Bake with It. I often substitute a tablespoon or two of coffee for liquids in brownies or chocolate cake. It adds a rich flavor without being overwhelming. A coffee ice cube, by the way, is typically 2 tablespoons of liquid, so you can just throw one of those in with the liquid.
One more coffee-related tip I found on Pinterest, my new favorite time-suck: You can make your own vanilla coffee creamer, without all the unpronounceable ingredients, by heating up in a small saucepan 1 can of sweetened condensed milk and 1-1/2 cups half and half, then whisking in 1 teaspoon vanilla creamer, and, if you want, 1/4 teaspoon cinnamon. When it cools, just store it in a jar in the fridge and use it, smugly, like you would Cremora.