I don't carry specifically for SD but always carry two on me: a folder clipped to my left pocket since I'm a leftie and a Leatherman Squirt P4 on my keychain in my right pocket to use around sheeple or to lend out. The mini Leatherman earned its place after it enabled me to wrestle a stripped pedal back onto my bike a fair distance out on a trail. Really handy little tool.
I also keep a Fallkniven S1 in the door of my car or in my pack if I'm walking for local trips and replace it with a custom Ranger RD7 for out of town trips (that one stays in the car unless hiking). It may get some strange looks if it ever came down to it but my pack also has a first aid kit, paracord, energy bars, water-resistant shell or sweater, lighter, and steel water bottle. In light of that stuff a fixed blade isn't out of place.