If I could carry a boxcutter with me at all times, I would. But the NYPD is known for hassling even tradesmen carrying conspicuous blades, so a lot of times I find myself trying to cut things with my fingernail or my keys.
Designed by Portland-based Amalgam PDX, the Quark has recently been crowdfunded. You can pre-order them here for $18 a pop (or cheaper if you buy in bulk).