Wouldn't it be nice if you could go backpacking for a week and be able to have an ice cold soda on that last day? Or to keep sausage and eggs cold for longer? Well for the total cost of less than 10 bucks you can! This is a cheap and effective DIY. The whole thing weighs barely anything even with 3 ice packs, you'll definitely be carrying more weight from the food you'll be keeping cold rather than the cooler and cooling packs themselves. This project will take you an hour or so and the payoff would still be worth it even if it took 10 hours.
Step 1: Materials
The materials in the picture are:
2 Thermal bags that I found at the dollar store, you can also find them at Costco and just about any supermarkets though.
Mylar emergency blanket, you can get 4 for $5 online or get them at Sport Chalet or any other camping supply store.
Cold packs, You can get the particular ones that I use from doctors offices who have medication delivered that needs to keep cool, or you can probably buy them at Costco or any supermarket, I like these ones because they keep cool longer than the plastic ones and they can be shaped by freezing them in whatever position.
Step 2: Making the Inner Bag
Take your scissors and one of those thermal bags and cut off the handle and then cut it right up the middle. Tape one of the sides that you cut closed (with the exception of the top of course, see picture 3 on this page). After you have half of it taped, place that inside of the other half of the bag and tape the long side closed, this will also hold the other piece in place and give it 2 good walls and make it doubly thick. When you put the one half inside of the other and after you tape the side, you're going to have to tape the openings. There are about 4 or 5 pieces of insulation on each wall and we have it twice as thick and there are two walls, so there are about 16 or 20 pieces of insulation so you need to divide how ever many there are by two and tape that many together on each side so the food goes in the very middle. The fifth picture is of the other bag, but if you look at it you'll understand what I mean. If you're only going on a short 2 day hike you can just freeze your hotdogs and throw them in this small bag with your already cold eggs and already cold sodas and they will be fine without a freezer pack even, but for longer trips you'll definitely want to go onto the next steps.
Step 3: Another Thermal Bag
The middle bag in the picture is what we're working on next. This one will only be 1 layer thick instead of 2, but this is what you'll keep the ice packs in to evenly disperse the coldness. This is made essentially the same way but don't double it up and make this one a bit thicker (I did it by cutting the handle off about 4 or 5 inches from the top and then taping that shut and cutting open one of the sides that's already sealed from the factory (so the opening is on what was originally a side. You'll keep your ice packs in this bigger bag and then put your smaller bag in this bag which will disperse the cold more evenly than if you just put the packs in. I suggest putting one pack on the bottom and then one in front of and one behind the bag for optimal contact. You can either be done here or make a Mylar bag to put that in which is optional, but I'll explain in the next step.
Step 4: Mylar Bag
I like this because the Mylar doesn't take up any extra space nor does it add any noticeable weight, yet it provides you with more options. I use the Mylar bag keep the other two in and if I'm going to be next to a creek or lake, I like to keep it in the creek to keep it cooler even longer. Mylar is an amazing material that can spread temperatures very well. Emergency blankets are made of Mylar because they're lightweight and thin so can be folded up really small yet can soak up temperatures and keep you warm, but if you surround it with cold, it has the opposite effect. If you put it in cold water it will make the things inside of it extremely cold. You could do this with the other bag but I prefer to do it with the Mylar because I believe it works better in water. All you have to do for this step is unfold your blanket (picture 2, doesn't it look cool?) then re fold it in half and half again the other way so it's a quarter of the size (4 thick). Then tape the ends together so it's just one sheet (like in picture 3) that's 1/4th the size. Then just get the second bag you made (the bigger one) and wrap it in this with plenty of extra room to take food and the ice packs into account. Then tape it up into another bag and you're on your way.
Step 5: Put It All Together!
Gather whatever you want to put in your cooler. I like to bring hot dogs, eggs and even a few cans of soda which never tastes as good as it does when you've backpacked several miles over several days.
Put it all into your smallest bag
Put an ice pack at the bottom of your other thermal bag, put your smaller bag into this bag, then put an ice pack in front of and behind that bag. Then put that bag into your Mylar bag and you're ready for some cold soda and fresh eggs even a week later!
If you're going to set this in a stream, tie the Mylar bag's opening shut with one end of a rope then tie the other end to a stationary object so it doesn't float away.