If you casually pick up a fish sandwich, you do nothing for your greater conforming to the image of Christ, Who chose to give up his life for you. However, you do not defy the Church that asks for some token self-denial. You do not do anything heroic even is the slightest degree, but you do not commit a mortal sin either.
Where is the complication?
There are just so many rules. Who can keep them all straight?