Although you do have to use the credits up by midnight of your checkout day, there are alternatives to just letting them go. You can get a lot of things with those credits that can be saved to use another day. Some food courts and CS places have cold sandwiches or other prepackaged meals that you could buy, put in your hotel fridge (if you have one), and save for the second half of your stay.
You could also use leftover snack or CS credits to "stock up" on drinks and snacks. Many resort shops allow a box of 12 donuts or a big bag of chips to be purchased with snack credits. And you can sometimes trade in CS credits for 3 or 4 snacks, or a beverage and 2 or 3 snacks. So you could pick up juice, milk, powerade, lemonade or any of several other beverages, along with fruit cups, desserts and/or chips. Then you'd only need to purchase the entree and you'd have a complete meal.