Every vehicle ought to equipped with such kit – for just in case.
The problem is, you'll have to put one together, yourself – because most modern cars haven't got any kit at all. Or even a spare tire, in many cases.
Here are some items you might want to have on hand for when just-in-case becomes now what?
What if you find yourself having to walk a distance in rain? Or maintain body heat, in the cold? You can buy survival ponchos and emergency blankets at camping/outfitter stores that fold into almost nothing, so take up next to no space in your vehicle's cargo area. Some warm gloves/socks/wool hats are a good addition to such kit, along with plastic bags big enough to house your feet. Put them on over your socks, to keep your feet dry (and warm) in the event your shoes get soaked.
Coolant kit –
For you and your car, both of which could overheat one day. Both can be addressed with water, which serves the same purpose as coolant – antifreeze – in a pinch. Since you can't (well, shouldn't) drink anti-freeze but your car's cooling system can "drink" water, keep that rather than a jug of coolant in the back somewhere.
Also a roll of silver duct tape, which is strong enough to contain a leak coming from a radiator hose and keep you mobile. If your car has a serpentine belt driving the accessories – such as the water pump as well as the alternator, air conditioner compressor and power steering pump – buy a spare in advance and keep it with the car. If the old belt frays and breaks, you'll be good to go. Serpentine belts require almost no tools to install – just the right-sized wrench or socket to lever the idler/tensioner down to remove/install the belt.