What's eaten at the seaside with bread that's old-fashioned now? (4,3,4)
I believe the answer is:
rock and roll
'old-fashioned now?' is the definition.
(old style of music)
'what's eaten at the seaside with bread' is the wordplay.
'what's eaten at the seaside' becomes 'rock' (eg Brighton rock).
'with' becomes 'and'.
'bread' becomes 'roll' (roll is a kind of bread).
'rock'+'and'+'roll'='ROCK-AND-ROLL'
'that's' acts as a link.
(Other definitions for rock and roll that I've seen before include "Two cakes" , "Musical genre" , "1950s' pop music" , "entertainment" , "Music genre" .)