Opening an umbrella indoors can't be helped sometimes. If it does, no big deal.
Black cat crossing your path is bad, but if you stop to pet it, and it starts purring, it negates the bad luck.
Smashing a mirror, hell if I know. It could be a problem if you cut yourself on the glass, but I don't know if it is bad luck or not.
Walking under a ladder, listen to me... DON'T EVER FUCKING DO THIS. I, myself have been riddled with bad luck for walking under a ladder once. I swear.
So yes, I am partially superstitious to the ones that have affected me. Mirror and umbrella? Nah. Cat and Ladder? Hell yes.