Sure-fire topics for easily striking up conversations with strangers:
With guys: Shaving
With new parents: Poop
With Pacific Northwesterners: Dietary restrictions
Approximately two-thirds of Seattle-area residents (a number I just made up) have some sort of dietary restriction, whether due to ideology, allergy, or both. If you're at a party just say "No thanks, I'm gluten-free right now" and you'll be off and talking with a bunch of the attendees. "Oh yeah, I have a gluten allergy too. These cookies are too good to pass up, though."
You can cross this with the new-parent poop topic: "Yeah, we're trying cutting lecithin and nuts from her diet; her poop was looking sort of greenish and she was howling at all hours of the night."
Thanks to preschool I now know that peanut allergies can be classified into airborne and contact variants. Parents take turns bringing snacks for the class and holy cow does that afford opportunities for dietary-restriction talk.
I have uncharitable theories about why this is. The Northwest is full of tech types who believe that religion is superstitious nonsense that is beneath them. Unfortunately for all of us, the universe is capricious and hard to understand, much less control. The urge to do both is within us all, though, and it finds its way out one way or another.
My related theory is that food allergies is a religion that does not set off the "no other gods before me" alarm in Judaism/Christianity/Islam. Thus it is a good mix-in religion. The Northwest is full of people who have been transplanted from all over the world. A mix-in religion is a great way to bond people of different faiths together.