Advert over railway for something to eat (4,6)
I believe the answer is:
puff pastry
'something to eat' is the definition.
(I have seen 'Lightweight food' mean 'puff pastry' so perhaps 'food' could also mean 'puff pastry')
'advert over railway' is the wordplay.
'advert' becomes 'puff' (as in a puff piece, type of advertisement).
'over' becomes 'past' (I've seen this before).
'railway' becomes 'ry' (abbreviation).
'puff'+'past'+'ry'='PUFF PASTRY'
'for' is the link.
(Other definitions for puff pastry that I've seen before include "Lightweight food" , "It's used for vol-au-vents" .)