I think for the general public, a portable shelter (heatsheet), some signalling (whistle/mirror) and a firestarter would be all I'd include.

I'd have, in BIG letters on the outside some basic advice (S.T.O.P or similar) plus a note that says 'Dress right, carry water, food, flashlight, pocketknife and tell someone where the hell you are going'

I'd guess 90% of the time sitting tight in the heatsheet and blowing the whistle is the best route for someone with no experience.