Book some public transport (7)
I believe the answer is:
omnibus
This clue is a double definition.
'book' is the first definition.
(I've seen this before)
'some public transport' is the second definition.
(omnibus is a kind of public transport)
(Other definitions for omnibus that I've seen before include "edition of book" , "Volume containing several books" , "Large public vehicle" , "traffic" , "Large vehicle - collected edition" .)