Murphy’s Laws are valid whether or not you believe in them, anyway… 
When it comes to dealing with Murphy I’m all in favor of Pascal’s Wager…
Also, I never walk under a ladder, if it looks like it might be unsteady…
Black cats, OTOH, are bad luck only if you happen to be a mouse! (Yes, I own one :eek: )
I have the nasty suspcicion that an entity of sort has inhabited my house key. Whenever I try to unlock the door, the key would get stuck and won’t turn at all, until I mutter the all-ecompassing swear word.
“WTF is wrong with this key!”
And then the key turns.
Wow, nothing bad has ever happened to you while carring the Q of H? Totally amazing.
I sometimes find myself yielding to superstition - but then I catch myself and take corrective action. Like subconsciously taking an extra long stride to miss a few sidewalk cracks. As soon as I realize what I’m doing and how stupid I feel, I make sure I step on every crack from that point onward. Thus far, mother hasn’t reported anything out of the ordinary.
Any time I feel tempted to yield to superstition, I chastize myself for losing my grasp on rationality.
Mine is inherited from my mother. Rabbit has to be the first thing that I say on the first of every month. Which is supposed to give good luck for the month. BTW this month when I said it I was walking to the bathroom for my shower, I looked out the window and there was two rabbits sitting in my backyard, so I must get super good luck this month 
Strangely enough, Friday the 13th has always turned out to be a good day for me. So, whenever a 13th happens to fall on that particular day of the week, I usually expect a good day, which is probably one of the reasons I generally have a good day on those days.
As for any other superstitions, don’t really have 'em, except I’ve noticed that a) if I’m in the process of writing a note to someone at work, they’re bound to get out of their meeting and show up, making the note obsolete; and b) if I’m about to get into the shower or don’t want to talk to anyone for any other reason, my mother or sister, both notorious talkers (think about an hour on the phone each) are bound to call. I think that’s more Murphy’s law though.
Oooh, one more I almost forgot: I know intellectuall that nothing’s going to happen, but after hearing that “Bloody Mary” story when I was a little kid and having my sister scare the living bejeezus out of me, I still can’t stand in front of a mirror in the dark. I’m 29 now. It’s ridiculous.
(For the uninitiated, the Bloody Mary story is about a girl named Mary who goes somewhere (I think on a date) wearing a white dress with a white ribbon around her neck. She gets her head sliced off and dies, then comes back, puts it back on her shoulders, securing the head with her white ribbon, now turned red from all the blood. Children love to scare each other by saying that if you stand in front of a mirror in the dark and chant “Blood Mary” over and over, she’ll show up in the mirror, bloody ribbon, heading falling off and all. My sister made me go into the bathroom and do this once and managed to create a clever enough trick that I’ve been traumatized ever since. )
Knocking on wood. I know it’s silly, but if I boast of some good luck, I have to find some wood to knock on or I worry the gods will punish me in some ironic way.
I have one superstition, one that I made up myself.
When you’re walking down a sidewalk at night and a streetlight goes out as you walk under it, that’s good luck.
Well, it keeps me safe from the big stuff, things that really throw your day for a loop, like accidents, unfriendly breakups, speeding tickets (Five years of driving, one ticket, and the judge dismissed it), theft, breakage, sickness (one sore throat a year, for about three days), hard drive crashes, cutting myself, or what-have-you. It doesn’t protect me from the minor, “that’s the price of living” stuff, like missing the BART and having to wait, slightly overcooking dinner, or getting turned down for dates. But yeah, it’s really cool. I can’t explain it.
To quote a fortune cookie I got one time:
It’s a bad day to be superstitious