Here is a kit I might carry on an overnight backpacking trip.

Its got the basics covered with:

Water: bags, tablets
Shelter: Space blanket, garbage bags(x2)
Fire: Matches(x2)
Signaling: Mirror, whistle
Tools: Knife, wire saw, compass on wrist band
First aid: sanitary napkin for stopping big bleeding) band-aids, gloves
Comfort items: Kleenex

NOTE: It has no food, as that attracts bears. The knife is a swiss army model with a locking blade. Looking it over, I would add:

Flagging tape,
sunblock chapstick,
Tyneol and pepto meds,
safetypins
cordage ( probably 50# test line)