Anything that's left behind, not eaten or used up, is unconsumed. After your picnic on the beach, you should wrap up any unconsumed sandwiches and take them home for dinner.
Restaurants work hard not to end up with unconsumed food that's in danger of spoiling, and if kids at school throw away what they don't eat, their parents won't ever know about their unconsumed carrot sticks and apples. This word is formed by adding the prefix un-, "not," to consumed, "eaten or used up."