If you're trying to stock your car with emergency food in case you get stuck somewhere, keep in mind that summer temperatures can wreak havoc on anything stored in your trunk. Emergency kit instructions often say to have some water and snacks on hand in addition to jumper cables and other auto supplies, but the instructions don't tell you what foods could pose safety issues if left in a hot trunk for weeks. This is partly because it's difficult to tell what might go bad; temperature variations and the age of the food when you put it in the trunk -- plus any existing food safety problems lurking in the packages -- can all make a food more or less likely to spoil in the heat. However, there are a few guidelines you can keep in mind.

Long-term Storage for Short-term Use

Remember that your car emergency food is meant to tide you over if you get stuck somewhere or if you find you have to walk home a great distance. For most people, this would cover something like finding out the power in the city is out, creating so much traffic that they have to stay where they are for a few hours. If you're planning a trip somewhere where there's the potential to be stuck for several days -- such as planning a trip when a snowstorm might blow through in winter -- then you have to adjust the amount of food you carry. But for your typical office worker who just needs something edible, a few packs of portable, nonperishable food will do.

Dry Foods and Survival Biscuits

Car trunks can reach temperatures in the 120s and even 140s Fahrenheit in summer, depending on your location. Your food -- and its packaging -- has to be able to withstand that. Foods that are dry and that don't contain anything that could melt or mold are what you need to look for. Dry crackers and crunchy granola bars, for example, or even a few bars of emergency biscuits meant for life rafts could work. (Do check with the manufacturer of the emergency biscuits if they're able to sit in heat; many brands are because the emergency food has to withstand tropical temperatures, but you can't assume anything.)

If you have any regular passengers who have special needs, such as a child who has to eat gluten-free foods, remember to find foods that the person can eat.

Some Nonperishables Not Suitable

Nuts are risky. They can become rancid in heat, and while one or two days might not do anything, a few months in a hot trunk could ruin them. Chocolate is obviously bad, as it will melt, but that also means you can't have things like chocolate chip granola bars in there. Dried fruits can still form mold.

Surprisingly, MREs are not a good choice. These meals-ready-to-eat are meant to be portable, but they're not meant for long-term storage in heat. Their shelf life can dive to as little as one month if stored in a hot area.

Remember Beverages

Don't forget that beverages can suffer as well. Water stored in plastic bottles can begin to taste like the plastic, so you might want to look for emergency water rations stored in foil bags. These are available online and from survival stores.

Try to avoid juice boxes. While the juice boxes are supposed to be shelf-stable, they can develop mold inside, and it's impossible to tell since the packaging is not see-through.

Try to rotate foods and water out monthly if you can. Specialized emergency water bags and life raft biscuits may have longer storage lives, but for regular foods like crackers, try to change them out rather frequently to further avoid problems.