The only thing I've ever done to use up leftover CS credits at the end of a trip is to purchase 'cold' CS meals in the resort food courts to take with us to the airport - sort of an airport picnic lunch for later.
You can get sandwiches, fruit, potato chips, cookies, yogurt - all of this will pass through security at the airport.
You could do a similar thing if you are headed to the beach or someplace on those 'out' of Disney days - take sandwiches, fruit, sweets, bottled drinks with you wherever you are going on those days.