I’m looking for suggestions for snacks to store in the car for occasional use. Not for an imminent road trip, but rather a back up emergency snack reserve. So I’d like ideas for snacks that can endure a few months of hot or cold weather, and also will be palatable, or at least not actively disgusting, if consumed while hot or cold. So far all I’ve thought of are those little packages of cheese (or peanut butter) and crackers.
This looks like a good starting point.
Only thing I’ve found that hold up even remotely for more than a week is a sealed jar of sunflower seeds. Pretzels get stale, fast. Chips get rancid, candy melts or turns to plastic.
Nuts are always a good choice. Especially if they are vacuum sealed like Planters jars and cans.
Things that are individually sealed, like granola bars, ought to hold up for a few weeks.
OP said ‘snacks’ 
You can also get nuts in sealed plastic bags, such as these. Some granola bars contain chocolate or other stuff that’s going to melt in the heat.
Consider things you don’t normally like all that much, but can eat. This way you are not tempted to eat it unless you really need it.
Ha! In the book Blue Highways, an account of a man traveling around the country in a van, a friend gives him a case of cat (maybe dog) food, so that he will have something for a genuine emergency. Ain’t nobody eating that if they’re just bored.
I used to keep these kinds of crackers when I was transporting my granddaughter to her sitter. Even when they started getting a bit stale, they were still edible.
Jerky
Pemmican
dried fruit
Nuts in sealed bags
crackers in sealed bags
Emphasis on a good seal, otherwise they all will absorb moisture and go bad. You might put your sealed bags in a metal tin. That way you won’t attract mice.
Munch bars, chick-o sticks and hard candy hold up well overtime.
I’ve seen jerky go rancid after a couple of months in a hot car. And anything with chocolate melts.
Bridgford makes backpacking food that doesn’t need to be heated or need boiling water.
The first bite of the BBQ sandwich is surprisingly good. The next bite, you kind of have to convince yourself to swallow. You want to eat it with water. 
It would be good survival food.
Coincidentally, while cleaning out my garage I found a box of 120 of those (Planters brand) that were at least 20 years old (bought by the previous tenant). I did not try them, but they looked perfectly edible. Though I noticed that a mouse must have gotten to a few of them and given up… so maybe they were in worse shape than they looked.
This is excellent advice, at least for me. Otherwise I’d be restocking weekly.
I guess that would solve the how-long-will-it-stay-edible dilemma.
mmm
My recommendation is: don’t keep food in your vehicle.
Dry cereal.
Long shelf life, something you can eat dry, like Cheerios, and has actual nutrients in it. A couple of bottles of water, and you’re good to go.
(Just don’t get anything too yummy, think nutritious, so you don’t eat it all up, when feeling snacky!)
cans of tuna and cup o’ noodle
I don’t think the interior of a car gets above 170 or so in summer, but a gallon jug of water and some dehydrated food would be good. However in winter the water would freeze, and if the container doesn’t have extra space in it will burst.
A box of saltine crackers and a jar of peanut butter. And a knife.
Just be prepared to toss and replace both at least once a year, or if you’re organized, swap the car set into the house every six months and eat them.