Book stockpile (7)
I believe the answer is:
reserve
I believe this is a double definition.
'book' is the first definition.
(as in booking or reserving in advance)
'stockpile' is the second definition.
(I know that stockpile can be written as reserve)
(Other definitions for reserve that I've seen before include "Keep for someone - spare bod" , "Keep for future use" , "Book - substitute player" , "Book - spare player" , "Bank" .)