Lunch packed with punch? (7,8)
I believe the answer is:
knuckle sandwich
'punch?' is the definition.
('knuckle sandwich' can informally mean a punch)
'lunch packed with' is the wordplay.
I cannot really see how this works, but
'with' could be 'and' and 'and' is found within the answer.
This explanation may well be incorrect...
(Other definitions for knuckle sandwich that I've seen before include "Bunch of fives" , "piece of pork between slices of bread" , "Slug" , "Punch in mug" , "Buffet" .)