Something to eat with top boffin (7)
I believe the answer is:
egghead
'boffin' is the definition.
(I've seen this before)
'something to eat with top' is the wordplay.
'something to eat' becomes 'egg' (egg is a kind of food**).
'with' means one lot of letters go next to another.
'top' becomes 'head' (head is a kind of top).
'egg'+'head'='EGGHEAD'
(Other definitions for egghead that I've seen before include "Informal intellectual of ovoid type" , "Boffin" , "Ovoid-shaped intellectual" , "Brainbox" , "providing access to soldiers" .)