I asked this before and got a good answer. It was some type of military MRE type "brick of Calories". I want something I can leave in my Trunk bag that will still be useful and edible in the changing heat of the trunk.
Also how can I store water in my trunk?

Lifeboat rations


Water


Cheaper water

Write date on items and replace/ rotate annually.
A large jar of shelled sunflower seeds and a gallon of water in this.

I usually keep a case of water in my truck. I drink so much of it, especially in the summer that I don't have to try hard to rotate it through. If I need to dump it, oh well, $3 to replace, and its not in one big heavy container.

I really like cliff bars compared to any other option. They don't turn into a gooey mess in the summer, and you have flavor options. It's also nice to just eat one vs cracking into an MRE or a boat bar package if you just need a snack.

Millennium bars.

I keep a medium sized pelican cooler in the back of my SUV.    During the summer I swap out two 2-liter bottles with a couple of frozen ones from the freezer in the garage every day before I go to work.   The idea is to keep from temperature cycling the food and water every day.   Keeps everything cool all day, even in August.    I don't typically swap frozen bottles on the weekend.    By Monday AM the bottles are thawed but the contents are still cool.    Then I keep about two thirds of the cooler full of water and a third full of canned food and granola bars.    Water gets used reasonably often.    I often have a few candy bars as well.     Once you start using something like this it is funny how helpful it can be.

Ran into one of those late night family emergencies away from home.   Brother in law and I went outside to get some air and discuss things and the walk took us over next to my SUV.   I reached into the back, grabbed a water bottle, and handed him one.    He took it, said "thanks", and said "ITS COLD!!!!!!" like he was surprised that someone would keep cold water in their car......   Why would I want to drink warm water?  

In the winter (Northern US) I don't do anything with it (swapping bottles) and it hasn't frozen on me yet.

I also have a plastic, sealed container with a flashlight and some spare batteries in it as well.   Keeps them fresh that way.

It is one of those things that if I didn't keep it cold, I probably wouldn't use it as much.   But because it is there and is cold, I use it (and appreciate it) more.  

Then if I ever have to bail then I would have to transfer what I need (or want) to my bag and head out.

2Hut8

I use Datrex lifeboat rations and water. They have survived 5 years of 100F summers and freeze/thaw winters. Both tasted fine when rotated out at the 5 year mark. All other water options leaked during the first winter. I would try the rations and pick one that is both palatable and easy on your digestive track. My wife and I found Datrex to be the best compromise for both of those requirements.