Doing this keeps your food drier since you won’t have ice melting into a pool of water, and you’re not wasting space with ice packs that you can’t eat or drink. If you’ll be staying somewhere with a freezer during your trip, save the bottles to refill and refreeze.
Normal plastic water bottles and milk jugs won’t explode when they freeze because they are built to expand. If you use a different kind of bottle, make sure you leave some air space to allow for ice expansion. Don’t use glass bottles; there’s a breakage risk and they’re heavy. If you’re buying ice, take it out of the retail bag and repack it in Ziplock bags to reduce meltwater messes. You can also freeze your own water in Ziplock bags; lay them flat in the freezer to make ice thick sheets.
Some people worry about carcinogens or other toxins from freezing or using plastic water bottles. There’s [no](http://cancer.about.com/od/cancercausesfaq/f/freezingwaterbo.htm) [need](http://www.jhsph.edu/dioxins) [to](http://www.plasticsmythbuster.org/main-menu/plastics-rumor-registry/freezing-plastic-water-bottles-releases-dioxins-into-water-)
1. **Wash your cooler well** before use and before storage with warm, soapy water. Vinegar or a water-bleach solution can help banish smells.
1. **Make sure you pre-chill all the food** before you put it in the cooler. If your food can be frozen without affecting the quality (milk, most soups, chilis, etc.) and you won’t need it right away, freeze it. You can freeze juice boxes or pouches; they are designed to not burst. Don’t freeze canned beverages/foods. To save space and weight, freeze your soup/chili in a freezer bag that has been placed inside a pan; leave the pan at home and put your pan-shaped bag of food in the cooler. Note that milk, cheese, and certain other foods will change texture/mouthfeel if you freeze them; read up on the freezability of your foods if you’re concerned about this. Milk will have to be completely thawed before drinking.
1. If you have a large freezer with enough room, **freeze your entire cooler** for a few hours before loading it. If your freezer isn’t that big, you can pre-cool your cooler putting some ice in it for 6+ hours. Dump out the meltwater and dry it out, then load it up. At the very least, bring your cooler down to room temperature with the lid open if it’s been stored in a hot location.
1. If you have access to an industrial freezer (restaurant, grocer, cafeteria), freeze everything you can in that. Industrial freezer get much colder than residential freezers. It won’t make a *huge* difference, but it does help somewhat.
1. **For some cool drinking water at the start of your trip**, freeze some half-full bottles and then fill them up with cold water just before you put them in the cooler.
1. One large cooler will generally keep your food colder than two smaller ones, but having a **separate cooler for beverages** may help your perishable food stay cold longer, since there will be fewer lid openings that let hot air in. Or have a separate cooler for dairy/meat, which are more prone to spoilage.
1. **Pack related items together inside a large ziplock bag**, such as condiments or sandwich ingredients, or everything you’ll need for a certain meal. That way it’s easier to find everything you need quickly so the cooler is open for shorter times, and the food will stay drier. Pack what you’ll need first at the top of the cooler. Throw in a few extra bags to store leftovers. Foods that come in a “resealable” package will probably not stay dry if they get submerged in meltwater once they’ve been opened; put them in a ziplock bag.
1. Plastic **egg carrier cases** work well, but they take up a lot of space even when they’re almost empty. (Two small carriers is better than one large one!) A cardboard egg carton inside a plastic bag is fine as long as you’re careful not to crush it, and if space is needed you can cut off the unused cells. Hard-boiled eggs can be pre-peeled and kept in a ziplock bag. If you’re making scrambled eggs, pre-mix them and put them in a tight-sealing container or wide-mouth bottle. It is possible to freeze eggs too, but [with some preparation](https://www.google.com/search?q=freeze+raw+eggs). (If you live outside of the U.S., where your [eggs are unwashed](http://www.forbes.com/sites/nadiaarumugam/2012/10/25/why-american-eggs-would-be-illegal-in-a-british-supermarket-and-vice-versa/), you don’t need to keep your unbroken eggs in the cooler unless you’re somewhere *really* hot.)
1. Wash and dry raw fruits and vegetables before you leave. Vegetables can usually be cut ahead of time too. Partially prepare recipes when possible.
###Keeping it Cold:
1. If you don’t use frozen water bottles but opt for ice instead: **draining the meltwater** may be beneficial for sanitary reasons (cross contamination risk) but keeping it helps the cooler stay cold longer. *Ice chips and shaved ice melt faster than block ice.* Consider repacking ice into Ziplock bags when you buy it.
1. **Keep your cooler out of the sun, and don’t leave it in a hot vehicle** if you can safely store it somewhere else. If it does have to stay in the sun or a vehicle, cover it with a blanket, towel, sleeping bag, or shade it with a tarp or reflective emergency blanket. (If you’re camping, don’t leave your cooler in your tent or outside. Hungry animals and/or people will show up.) If you cover it with a dampened towel, evaporative cooling will help too.
1. **Keep a thermometer in your cooler.** Your food should stay below the “[danger zone](http://en.wikipedia.org/wiki/Danger_zone_(food_safety))” temperature of 5°C / 41°F. Foods that are potentially hazardous if they spend two or more hours in the danger zone are: meat, fish, poultry, eggs, protein rich foods, dairy products, cut or peeled fresh produce, most cooked foods, shellfish, sauces and gravies, sprouts, and any foods that contain any of these items.
1. For long trips, and/or if you need food to stay frozen, **consider using dry ice** (known as “card ice” in some places), which is carbon dioxide frozen at -109.3°F / -78.5°C. Dry ice is non-toxic but it can cause rapid frostbite, asphyxiation, and other problems; read more about [safely handling and storing dry ice](http://www.dryiceinfo.com/safe.htm) before you buy. Dry ice *can* go in your main cooler if wrapped in a towel, but a more convenient option is to have a second cooler with just dry ice and frozen water bottles (and any food you want to keep frozen); transfer water bottles to the main cooler as needed. If you plan to use dry ice, also read about [quantity needed, packing, and transport tips](http://www.dryiceinfo.com/camping.htm).
1. In sunny weather, your parked vehicle can get really hot, really fast. You can **use a dry cooler for heat-sensitive items**, such as phones, cameras, and other electronics. The inside of the cooler will stay at ambient temperature for many hours even if your car’s interior hits 140°F / 60°C. If you have an extra dry cooler and enough space, you may wish to chill other food items that don’t require refrigeration, such as bread and apples, too keep them fresher.
1. **Avoid adding warm food or beverages.** It will bring the average temperature of the cooler way up.
1. You can purchase a **powered cooler** that is essentially a small 12v refrigerator. Be careful not to drain your battery, however; some vehicles keep their 12v power outlets live even when the vehicle is off.