Five Ways to Practice Mortification Without Outing Yourself as a Catholic
Although, it is good to give witness that one is a Catholic, i.e. saying grace in a public restaurant, I think the writer's point here is to make sacrifices that only God will know about. So that any good works will be hidden away from anyone but Him. You will be storing treasures in Heaven.
Be sure to read the comments for more ideas on mortifications you can do.
H/T to Barb