For a U-PSK....

-A small spool of dental floss (I think you can sometimes find 50' rolls) or a sewing machine bobbin of GOOD thread (or 20# braided fishing line), a couple of buttons and a few needles with eyes big enough.
-Duct tape, 4-6'
-Whistle (and one on your keys)
-asprin
-immodium
-change, small bills
-button compass
-small flashlight (and one on your keys)
-3-4' of wire
-paper and pencil

That should fit in an altoids tin or a pouch like the AMK pocket kits come in.

Honestly, it wouldn't hard to take a PSP and pull out the fishing kit, mirror, sparklite and tinder, and swap in the cash, light, and meds. Keep the safety pins and sewing needle in their vial, maybe add a couple of screws for glasses if needed, along with the buttons.

Add that to a small SAK or a compact multi with scissors, good boots laced with paracord, a small fak (AMK's .3 or .5 would be perfect), and a contractor bag or two. That fits in the pockets of most jackets, or the bottom of a bag or day pack with ease. Carry a water bottle.

The pyro in me NEEDS to have a lighter or a ferro rod, but I live in a state that doesn't have any one city with more 20K people in it, so I'm always thinking of the woods.

Scaling up, add a full sized multi or a pair of pliers. Pocket knife. Map. More change and cash. Better flashlight or a small headlamp. Poncho and/or heatsheet/space blanket. More duct tape/wire/paracord. Small strobe. Pepper spray and/or a sidearm, or a stout walking stick or umbrella.