The three items that I always have on my person are: Cell phone, Spyderco Paramilitary 2, and my wallet of course.
Optional/in my backpack: Laptop, phone/laptop charger, emergency cash, notepad, pens, pencils, small first aid kit, bottle of water, clif bar and/or some snacks, leatherman multi-tool, bottle/can opener, can of fix-a-flat, my glasses, glowsticks, flashlight, AA batteries, pair of thermals, hand warmers, mylar blanket, small fire extinguisher, USB drive, paracord, lip balm, FRX3 emergency radio, and a lifestraw.
I'm on the road a lot so my ever day "carry" (not usually carried, just left in the car) is probably more extensive than most.