If something is spareable, it means it can be kept in case it is needed later.
Spareable things are usually not very important, but it's good to have them just in case.
Examples:
The extra pencils are spareable.
Is this food spareable?
I have some spareable time this afternoon.
I always keep some spareable money in my bag.
She has spareable clothes in case it gets cold.
It's good to have spareable things in case of an emergency.