Grab a picnic with roll (3)
I believe the answer is:
bap
'roll' is the definition.
(I've seen this before)
'grab a picnic with' is the wordplay.
'with' says the answer is hidden in the clue.
'BAP' can be found hidden inside 'grab a picnic'.
(Other definitions for bap that I've seen before include "A soft flat bread roll" , "Flattish bread roll" , "Big roll" , "Large soft bread roll" , "Large flat round roll" .)