The needed tools will vary greatly by venu and circumstances. Most situations that are coming to my mind require a knife or safer cutter, a first aid kit just in case, appropriate environmental insulation or modification (heat, light, weather) and hand/foot/eye/breathing protection to start with.
Scenarios:
Car wreck, passengers trapped by seatbelts:
seatbelt cutter or one hander knife real handy, not buried in pocket or glovebox
glass breaker maybe
FAK
Cell Phone - handy, not crushed under dashboard in handsfree cradle...
fire extinguisher? Used to have palm size halon unit that I carried everywhere.

Earthquake at home, moderate damage:
Gas and water turnoff tool
Flashlights, not candles or oil lamps
One had opening knife, preferrably one hand closing also.
dust mask for the breathing impared at least
whistle and cellphone in the hand(s) of anyone trapped
Glass proof shoes for anyone able to walk
Broom
Gloves
"Bottled" water because water pipes busted and would have to boil with shutoff gas stove anyway...
lots of superglue, plastic and duct tape...

Interstate gridlock/accident, stuck on exit ramp for 4 to 14 hours (been there)
Extra gas or keep the tank fullish at all times
PortaPotty or reasonable substitute for climate and culture
Water
Jumper cables or portable battery for the car in front that ran the radio and lights till the battery died...
Blankets/Sleeping bags for all passengers to conserve gas in winter
CO and low oxygen detecter in car to avoid death from snow blocked tailpipe
Bolt cutters for opening alternative exits for the ambulance...


Flat tire, cold, dark, rainy night out of celphone coverage:
good spare
Jack
Tire Iron
Block for under jack
Flashlight,flares/lightsticks
Poncho
Gloves

Plane Crash or misplacement:
Doug has this covered quite nicely elsewhere... <img src="images/graemlins/wink.gif" alt="" />