Not quite grasping it. Think along the lines of Captain Tylor.
I suppose luck would best be represented by extra karma, which you can use to to have all sorts of lucky things happen (you can PM requests, a lot of people use karma reactively to have things like bullets getting stopped by something in your shirt pocket or whatnot).
Bad luck could be less karma...but that might not work so well, and you might die too fast. I'd probably rather have it either be something you RP yourself, oooooor maybe an offer to let the GM fudge dice rolls and hose you over should it amuse them at some point.
Curious what your thoughts are for good/bad luck advantage/flaw for Nightmarchers is. For example, sets off a trap but manages to stand in just the right area while those around him aren't so lucky.