It is almost impossible to predict what you are going to need if you get stranded.
If you end up in the ocean you would obviously need something to keep you afloat.
On snow and ice you would increase your survival chances with a shovel and a
snowsaw. In woodland you need an axe. A very sharp axe can also be used as a knife.
But maybe we should not forget the obvious like a good sleeping bag and
a tarp to keep you warm and dry. In every car you can find some room for a
cheap sleeping bag and a piece of plastic. The very compact bags you even can take
with you on a plane and can come in handy when stranded at the airport. Ad a bic lighter, a
bottle of water and a FAK and you can deal with a lot of common "emergencies".