I keep some canned beans, canned peaches and canned sardines in the trunk of the car. I don't like them inside the car because I don't like things that can turn into missiles if I am in a crash.
Inside the cab I usually have a stash of chocolate bars and some hard candy.
My sister-in-law keeps a few bags of granola style trail mixes and dried fruit slices.

I like the canned stuff because iron rations are almost indestructible and come in many flavours. It helps to write what they are on the end of the can with marker just in case the labels come off.
Tinned food is pretty cheap too. Most of the time it does not even need heating, and it usually gets used and replaced frequently enough that expiry dates are not a problem.
The only special tools are a can opener and a table spoon.